Radiocapitellar and Ulnotrochlear Pressures Increase in a Radial Head Fracture Model: A Cadaveric Biomechanical Analysis.

BACKGROUND: Changes in intra-articular pressure have not been previously described in relation to the management of radial head fractures. We hypothesized that pressure within the radiocapitellar and ulnotrochlear joints would increase with progressive radial head resection, mimicking a displaced radial head fracture, in a cadaveric model. METHODS: Ten cadaveric specimens were tested. Intra-articular pressure sensors were used to measure pressure within the radiocapitellar and ulnotrochlear joints with the forearm in full supination. The elbow was loaded to 100 N in extension, 45° of flexion, and 90° of flexion under the following conditions: (1) intact radial head, (2) 20% radial head resection, (3) 40% radial head resection, and (4) 100% radial head resection. RESULTS: The distribution of pressure between the radiocapitellar and ulnotrochlear joints did not change with sequential, partial resection of the radial head (radiocapitellar joint, between 48.92% and 53.79%; ulnotrochlear joint, between 46.21% and 51.08%). After 20% resection, radiocapitellar peak contact pressure (PCP) increased by 22% (from 1,410 to 1,721.5 kPa) and ulnotrochlear PCP increased by 36% (from 1,319 to 1,797.5 kPa). After 40% resection, radiocapitellar PCP increased by 123% (from 1,410 to 3,145 kPa; p = 0.0003) and ulnotrochlear PCP increased by 105% (from 1,319 to 2,702 kPa; p = 0.007). Ulnotrochlear PCP increased by a total of 159% after complete radial head resection (from 1,319 to 3,415.5 kPa; p = 0.003). CONCLUSIONS: Pressures in the radiocapitellar and ulnotrochlear joints were equally distributed with an intact radial head and after partial resection. Radiocapitellar and ulnotrochlear pressures increased with increasing radial head resection, significantly exceeding 100% of normal after radial head resection of 40% of the anterolateral diameter. LEVEL OF EVIDENCE: Prognostic Level III . See Instructions for Authors for a complete description of levels of evidence.

Posterolateral Rotatory Instability Develops Following the Modified Kocher Approach and Does Not Resolve Following Interval Repair.

BACKGROUND: The modified Kocher and extensor digitorum communis (EDC)-splitting intervals are commonly utilized to approach the lateral elbow. Iatrogenic injury to the lateral ulnar collateral ligament may result in posterolateral rotatory instability (PLRI). in the present cadaveric study, we (1) evaluated lateral elbow stability following the use of these approaches and (2) assessed the accuracy of static lateral elbow radiographs as a diagnostic tool for PLRI. METHODS: Ten matched-pair cadaveric upper-extremity specimens (n = 20) were randomly assigned to Kocher or EDC-splitting approaches. Specimens underwent evaluation pre-dissection, post-dissection, and following repair of the surgical interval. Clinical evaluation of lateral elbow stability was performed with the lateral pivot-shift maneuver. Radiographic radiocapitellar displacement was evaluated with the fully extended hanging arm test and on lateral elbow 30° flexion radiographs. Paired Wilcoxon signed-rank tests with Bonferroni correction were utilized to compare groups. RESULTS: All Kocher group specimens (10 of 10) developed PLRI on the pivot-shift maneuver following dissection. No EDC-splitting group specimens (0 of 10) developed instability with pivot-shift testing. The fully extended hanging arm test showed no difference in radiocapitellar displacement between groups (p > 0.008). Lateral elbow 30° flexion radiographs in the Kocher group showed an increased radiocapitellar displacement difference (mean, 8.46 mm) following dissection compared with the pre-dissection baseline (p < 0.008). Following repair of the Kocher interval, the radiocapitellar displacement (mean, 6.43 mm) remained greater than pre-dissection (mean, 2.26 mm; p < 0.008). In the EDC-splitting group, no differences were detected in radiocapitellar displacement on lateral elbow radiographs with either the fully extended hanging arm or lateral elbow 30° flexion positions. CONCLUSIONS: The Kocher approach produced PLRI that did not return to baseline conditions following repair of the surgical interval. The EDC-splitting approach did not cause elbow instability clinically or radiographically. The hanging arm test was not reliable for the detection of PLRI. CLINICAL RELEVANCE: The Kocher interval for lateral elbow exposure results in iatrogenic PLRI that is not detectable on the hanging arm test and that does not return to baseline stability following repair of the surgical interval.

Diagnosis of traumatic shoulder arthrotomies using saline load test with intra-articular pressure monitoring.

PURPOSE: The purpose of this study was to investigate the amount of saline required to identify a positive traumatic shoulder arthrotomy in a cadaveric model. In addition, intra-articular pressure monitoring was conducted to confirm needle placement and evaluate peak pressure curves prior to capsular failure. METHODS: We conducted a cadaveric study using thirty fresh-frozen upper extremities with maintained glenohumeral joint. A shoulder arthrotomy was made in the deltopectoral interval using a 4.4-mm trocar. The joint was loaded using an 18-gauge spinal needle inserted posteriorly and attached to a pressure monitoring system. Fluid was introduced at a uniform rate of 1 cc/sec until active extravasation was visualized from the anterior arthrotomy site. Statistical analysis included assessment of distribution, ANOVA and linear regression. RESULTS: A positive joint challenge was obtained in all specimens (n = 30) within a maximum of 59 ml of fluid (mean 28 ml, STD 15.4). Average intra-articular pressure at visualization (PAV) was 166.8 mmHg (min., 107; max., 268). In twelve specimens, peak pressures (PP) exceeded PAV, showing a corresponding fall in pressure prior to visualization (ΔPP-PAV = 16.5). To reach a sensitivity of 90% and 95% of arthrotomies, 50 and 58 ml of fluid had to be injected. CONCLUSION: Results demonstrated 58 ml of fluid was required to identify a majority of shoulder arthrotomies. Intra-articular pressure monitoring identified successful needle placement. Pressure curve analysis could identify capsular failure before fluid extravasation visualization which could enhance clinical identification and treatment of traumatic shoulder arthrotomies. LEVEL OF EVIDENCE: Level IV Diagnostic.

Efficacy of Cefazolin Versus Vancomycin Antibiotic Cement Spacers.

OBJECTIVE: Cefazolin is a heat-labile antibiotic that is not usually added to polymethylmethacrylate (PMMA) cement spacers because it is believed to be inactivated by the high polymerization temperatures. The purpose of this study was to compare cefazolin versus vancomycin high-dose antibiotic cement spacers. METHODS: High-dose antibiotic PMMA spacers with either cefazolin or vancomycin were fabricated. Setting time, compressive strength, and compression modulus of spacers were measured. Spacers were emerged in saline, and the eluent was tested on days 1, 2, 3, 7, 14, and 30 to determine the zone of inhibition of methicillin-sensitive Staphylococcus aureus and estimate the cumulative antibiotic released. RESULTS: Cefazolin, compared with vancomycin-loaded spacers, had significantly shorter setting time [mean difference (MD) -1.8 minutes, 95% confidence interval (CI), -0.6 to -3.0], greater compressive strength (MD 20.1 megapascal, CI, 15.8 to 24.5), and compression modulus (MD 0.15 megapascal, CI, 0.06 to 0.23). The zone of inhibition of eluent from PMMA-C spacers was significantly greater than PMMA-V spacers at all time points, an average of 11.7 ± 0.8 mm greater across time points. The estimated cumulative antibiotic released from cefazolin spacers was significantly greater at all time points ( P < 0.0001). CONCLUSIONS: Cefazolin was not inactivated by PMMA polymerization and resulted in spacers with superior antimicrobial and biomechanical properties than those made with vancomycin, suggesting that cefazolin could play a role in the treatment of infected bone defects with high-dose antibiotic PMMA spacers.

Single- and Double-Loaded All-Suture Anchor Repairs of Anteroinferior Labral Tears Are Biomechanically Similar in a Cadaveric Shoulder Model.

Purpose: To compare the biomechanical strength of single- versus double-loaded all-suture constructs in an anteroinferior glenoid labral repair. Methods: Anteroinferior labral lesions were created on 6 matched pairs of cadaveric shoulder specimens. Each shoulder in a matched pair was randomized to either receive capsulolabral repair with 3 single-loaded all-suture anchors or 3 double-loaded all-suture anchors. Immediately following capsulolabral repair, the specimens underwent mechanical testing, which included cyclic testing (5 N to 50 N for 500 cycles) and load-to-failure testing (rate of 15 mm/min). The gap formation between the repaired labrum and glenoid (measured at 1, 25, 100, and 500 cycles), the load at 2-mm gap formation, the maximum load at failure and the method of failure were recorded. Data were analyzed with paired Student t tests and Bonferroni correction factor. Results: The single and double all-suture constructs did not differ significantly in gap formation at any number of cycles, load to 2-mm gap formation (P = .75), or maximum load to failure (P = .46) between the 2 groups. Conclusions: In this study, single-loaded and double-loaded all-suture anchor constructs demonstrated comparable biomechanical performance and did not significantly differ in gap formation, load to 2-mm gap formation, or maximum load to failure when used in the capsulolabral repair of anteroinferior glenoid labral tears in human cadaveric specimens. Clinical Relevance: Although studies have evaluated the biomechanical properties of various arthroscopic labral stabilization techniques, the biomechanical properties of all-suture anchors with regard to labral stabilization are not well understood.

Ligament-Sparing Volar Radiocarpal Arthrotomy During Distal Radius Fracture Repair: Anatomical Description and Quantification of Articular Surface Area Visualized in a Cadaveric Model.

PURPOSE: Distal radius (DR) fracture repair using the volar locked plating technique typically involves indirect fracture reduction, assessed using fluoroscopy, without direct visualization of the articular surface. This method of fracture repair may be guided by the rationale that volar radiocarpal ligament disruption may cause radiocarpal instability, although direct articular visualization may facilitate improved fracture reduction. This study investigated anatomical feasibility and articular surface visualization using volar ligament-sparing radiocarpal arthrotomy pertinent to DR fracture repair. METHODS: Ten fresh-frozen cadaveric specimens of the upper extremity underwent volar arthrotomy via the standard flexor carpi radialis approach with partial longitudinal sectioning of the long radiolunate and partial transverse sectioning of the short radiolunate ligaments to visualize the articular surface of the DR. Following arthrotomy, the visible surface of the DR was analyzed using digital photography. The wrist was disarticulated, and the fully exposed articular surface was photographed. The visible area of the articular surface was quantified using digital imaging software by calculating the ratio of the surface area visualized using the arthrotomy to the total articular surface area. RESULTS: The percentage of the articular surface area of the DR visualized using the volar arthrotomy was 76% ± 7.6% (range, 69%-90%), including both the scaphoid facet, lunate facet, and scapholunate ridge. CONCLUSIONS: Volar radiocarpal arthrotomy allows clinically relevant visualization of the articular surface of the DR, including the scaphoid and lunate facets. CLINICAL RELEVANCE: Radiocarpal arthrotomy may facilitate improved articular reduction during DR fracture repair via the volar approach.

Tensile strength of a novel superficial suture pattern compared to traditional suture patterns in a cadaveric human skin model.

BACKGROUND: The suture material and pattern utilized to maintain the skin edges in proximity allows for successful primary wound healing. No prior studies have evaluated the tensile strength of different suture patterns on human cadaveric skin. This study evaluates the tensile strength of four single suture patterns: simple (S), horizontal-mattress (HM), vertical-mattress (VM), and a novel stich termed Lindeque locking (LL). METHODS: Four skin closure patterns were tested on human cadaveric skin using 3-0 nylon - S, HM, VM, LL - totaling four groups with twelve samples each. A tensioning device applied 1 N of force/second in a linear fashion. The primary outcome measures were: (i) wound dehiscence force, and (ii) ultimate load to failure. Statistics included one-way ANOVA with post-hoc Tukey tests. RESULTS: The LL stitch had the greatest dehiscence force (198.60 N) and ultimate load to failure force (211.13 N) but was only significantly greater on both outcomes versus HM (104.81 N; 95% confidence interval [CI], 65.7 to 121.9; p< 0.001) and (120.79 N; 95% CI, 63.5 to 117.2; p < 0.001), respectively. There was no significant difference between LL and S for dehiscence, nor for the ultimate load to failure (186.90 N and 195.08 N, respectively). The LL pattern was significantly greater for an ultimate load to failure, but not for dehiscence when compared to VM (173.9 N and 171.1 N, respectively). Of all patterns, HM had significantly less withstanding force. CONCLUSIONS: The Lindeque Locking stitch demonstrated the greatest dehiscence force and tensile strength. It may decrease the risk of wound dehiscence for high tension wounds.

Two Orthogonal Nitinol Staples and Combined Nitinol Staple-Screw Constructs for a First Metatarsophalangeal Joint Arthrodesis: A Biomechanical Cadaver Study.

BACKGROUND: End-stage hallux metatarsophalangeal (MTP) joint arthritis is commonly treated with arthrodesis using stainless steel or titanium implants. These implants provide static compression that is maximal at the time of implant insertion. Alternatively, nitinol staples are capable of dynamic compression. They have most frequently been used for midfoot arthrodesis procedures. However, their biomechanical performance during hallux MTP arthrodesis has not been described. METHODS: 8 matched pairs of cadaveric feet (4 female, 4 male) were prepared for hallux MTP arthrodesis using cup and cone reamers. Cadaveric pairs were then instrumented with either (1) a transarticular lag screw and dorsal nitinol staple or (2) orthogonal nitinol staples placed dorsally and medially. Walking in a short leg cast for 6 weeks was simulated by applying 90-N forces at 3 Hz to the plantar proximal phalanx for up to 250 000 cycles. Failure was defined as catastrophic implant failure or plantar gapping beyond 7 mm. RESULTS: 15 of 16 specimens failed cyclic loading. All 8 specimens fixed with orthogonal staples failed at an average of 37 ± 81 cycles. 7 of 8 specimens fixed with a dorsal staple and crossed screw failed at 14 900 ± 39 000 cycles. Collectively, 5 specimens failed because of bone fracture (1 in orthogonal staples, 4 in staple-screw group) and 10 failed because of excessive gap formation (7 in orthogonal staples, 3 in staple-screw group). The number of cycles to failure was significantly lower (P = .0469) in the orthogonal staple constructs compared with the dorsal staple and crossed screw constructs. CONCLUSION: The tested constructs permit significant motion at the first MTP fusion surface during simulated protected weightbearing. Although multiple in vivo factors should be considered when extrapolating results from this cadaveric study, this motion may result in clinical failure with early postoperative weightbearing protocols. CLINICAL RELEVANCE: We report the first biomechanical evaluation of hallux MTP arthrodesis using modern nitinol staples in 2 separate constructs.

Blockade of Osteoclast-Mediated Bone Resorption With a RANKL-Inhibitor Enhances Bone Formation in a Rat Spinal Fusion Model.

STUDY DESIGN: Rat spine fusion model. OBJECTIVE: The present study aimed to determine whether administration of osteoprotegerin (OPG) in a rat model of spinal fusion increases bone volume, bone density, and decreases osteoclasts in the fusion mass. SUMMARY OF BACKGROUND DATA: OPG is a soluble RANK-ligand inhibitor that blocks osteoclast differentiation and activation. This makes it a potential agent to control the remodeling process and enhance bone mass during spinal fusion. MATERIALS AND METHODS: Forty-eight male Sprague-Dawley rats received a one-level spinal fusion of L4-L5 with bone allograft. Rats were then divided into four groups according to initiation of treatment: (1) saline on day 0 (saline), (2) OPG on day 0 (OPG D0), (3) OPG on day 10 (OPG D10), and (4) OPG on day 21 (OPG D21) postsurgery. After their initial injection, rats received weekly subcutaneous injections of OPG (10 mg/kg) and were euthanized six weeks postsurgery. MicroCT analysis of the fusion site and histological analysis of bone surface for quantification of osteoclast lining was performed. RESULTS: Increased bone volume in the fusion site and around the spinous process was seen in OPG D0 and OPG D10 when compared with saline. Mean trabecular thickness was greater in all groups receiving OPG compared with saline, with OPG D0 and OPG D10 having significantly greater mean trabecular thickness than OPG D21. All OPG groups had less bone surface lined with osteoclasts when compared with Saline, with OPG D0 and OPG D10 having fewer than OPG D21. CONCLUSIONS: This study indicates that OPG inhibited osteoclast bone resorption, which led to greater bone at the fusion site. Future studies investigating OPG on its own or in combination with an osteogenic factor to improve spinal fusion outcomes are warranted to further elucidate its potential therapeutic effect.

Ligament-Sparing Volar Radiocarpal Arthrotomy During Distal Radius Fracture Repair: Biomechanical Implications on Wrist Stability in a Cadaveric Model.

PURPOSE: Distal radius (DR) fracture fixation with volar locked plating typically uses indirect fracture reduction without direct visualization of the articular surface in an attempt to preserve the volar radiocarpal ligaments and prevent iatrogenic radiocarpal instability. This study assessed the biomechanical stability after a volar radiocarpal arthrotomy for direct articular visualization for DR fracture repair compared to a standard trans-flexor carpi radialis approach without arthrotomy in a cadaver model. METHODS: Ten fresh-frozen upper extremity matched-pair cadaveric specimens were tested. For each pair, one limb underwent trans-FCR approach with a volar arthrotomy that partially sectioned the long and short radiolunate ligaments to visualize the DR articular surface (Group 1). The contralateral limb underwent standard trans-FCR approach without arthrotomy (Group 2). Following capsular repair (Group 1), all specimens (Groups 1 and 2) underwent biomechanical testing, including axial loading (22.2 N, 44.5 N, 89.0 N, 177.9 N), volar translational, and dorsal translation loading (22.2 N, 44.5 N, 89.0 N) to assess carpal stability using both fluoroscopy and motion capture. Ulnar carpal translation was assessed using the Gilula method, measuring radiographic lunate overhang from the ulnar edge of the lunate fossa relative to the full width of the lunate. Dorsal and volar translation were assessed by measuring lunate overhang with respect to the dorsal or volar radial cortex. To simulate fractures with dorsal radiocarpal ligament disruption, the dorsal capsule was sectioned, and the biomechanical comparisons were repeated. RESULTS: Ulnar translation of the lunate remained below 2 mm for both groups in all testing scenarios. No significant differences were identified in ulnar, volar, or dorsal translation with increasing loads between the groups. CONCLUSIONS: This volar ligament-sparing radiocarpal arthrotomy did not cause biomechanical radiocarpal instability. CLINICAL RELEVANCE: This arthrotomy may provide enhanced visualization of the DR articular surface during fracture fixation without causing iatrogenic wrist instability.

Biomechanical Comparison of All-Soft Suture Anchor Single-Row vs Double-Row Bridging Construct for Insertional Achilles Tendinopathy.

BACKGROUND: Two common operative fixation techniques for insertional Achilles tendinopathy are the use of all-soft suture anchors vs synthetic anchors with a suture bridge. Despite increasing emphasis on early postoperative mobilization, the biomechanical profile of these repairs is not currently known. We hypothesized that the biomechanical profiles of single-row all-soft suture anchor repairs would differ when compared to double-row suture bridge repairs. METHODS: Achilles tendons were detached from their calcaneal insertions on 6 matched-pair, fresh-frozen cadaver through-knee amputation specimens. Group 1 underwent a single-row repair with all-soft suture anchors. Group 2 was repaired with a double-row bridging suture bridge construct. Achilles-calcaneal displacement was tracked while specimens were cyclically loaded from 10 to 100 N for 2000 cycles and then loaded to failure. Linear mixed models were used to analyze the independent effects of age, body mass index, tendon morphology, repair construct, and footprint size on clinical and ultimate failure loads, Achilles-calcaneal displacement, and mode of failure. RESULTS: The suture bridge group was independently associated with an approximately 50-N increase in the load to clinical failure (defined as more than 5 mm tendon displacement). There was no difference in ultimate load to failure or tendon/anchor displacement between the 2 groups. CONCLUSION: This cadaveric study found that a double-row synthetic bridge construct had less displacement during cyclic loading but was not able to carry more load before clinical failure when compared to a single-row suture anchor construct for the operative repair of insertional Achilles tendinopathy. CLINICAL RELEVANCE: Our data suggest that double-row suture bridge constructs increase the load to clinical failure for operative repairs of insertional Achilles tendinopathy. It must be noted that these loads are well below what occurs during gait and the repair must be protected postoperatively without early mobilization. This study also identified several clinical factors that may help predict repair strength and inform further research.

The potential biomechanical advantage of lag by technique screw fixation of the posterior pelvic ring.

PURPOSE: Diastasis of the sacroiliac joint after pelvic ring injury is commonly reduced by lagging by design with partially threaded (PT) screws. There may be a biomechanical benefit to lagging by technique with fully threaded (FT) screws. The purpose of this study was to compare these two methods. METHODS: Twelve pairs of synthetic bone blocks were lagged together with 8.0-mm FT or PT screws. Maximum compressive and steady-state force was measured. Pullout force testing was performed. RESULTS: The maximum compressive force of FT and PT screws was not different [mean difference (MD) 32 Newtons (N), 95% confidence interval (CI) 124, 60)]; however, lagging by technique with FT screws resulted in significantly higher steady-state force (MD 83 N, 95% CI 165, 5) and pullout force (MD 634 N, 95% CI 778, 491). CONCLUSION: Lagging by technique with large diameter FT screws has a biomechanical advantage over lagging by design with PT screws.

Fixation of Transverse Acetabular Fractures With Precontoured Plates Alone Causes Fracture Malreduction: A Biomechanical Assessment.

BACKGROUND: Precontoured quadrilateral surface buttress (PQSB) plates have grown in popularity for acetabular fracture fixation. However, our experience has pushed us to hypothesize that their use as sole means of fixation may cause fracture malreduction. A biomechanical model was created to investigate this theory. METHODS: A transverse acetabular fracture was created and reduced anatomically in 18 synthetic hemipelvises. The reduced hemipelvises were fixated using 3 different techniques. Group A fixation included anterior and posterior column screws plus a suprapectineal pelvic reconstruction plate; group B models were fixed using a PQSB plate only; and group C models were fixed with an anterior column screw and a PQSB plate. Acetabular tracking points were placed before final fixation and used to quantify any postfixation displacement. One-way analysis of variance and Tukey HSD testing were used to determine the significant difference (P < 0.05). RESULTS: Models in group B had significant fracture displacement after final fixation when compared with group A and group C models. The average amount of displacement at the anterior column and within the acetabulum was 1.37 mm (95% CI, 1.08-1.65) in group B constructs compared with 0.32 mm (95% CI, 0.22-0.42) and 0.26 mm (95% CI, 0.15-0.38) in groups A and C constructs, respectively. There were no significant differences in displacement after final fixation between group A and group C models. CONCLUSIONS: PQSB plates for acetabular fractures cause malreduction when applied in isolation in this biomechanical model. If a PQSB plate is chosen for fixation, we suggest the use of a columnar lag screw at minimum to hold reduction before plate application.

The CFL fails before the ATFL immediately after combined ligament repair in a biomechanical cadaveric model.

PURPOSE: To assess the impact on ankle stability after repairing the ATFL alone compared to repairing both the ATFL and CFL in a biomechanical cadaver model. METHODS: Ten matched pairs of intact, fresh frozen human cadaver ankles (normal) were mounted to a test machine in 20.0° plantar flexion and 15.0° of internal rotation. Each ankle was loaded to body weight and then tested from 0.0° to 20.0° of inversion. The data recorded were torque at 20.0° and stiffness, peak pressure and contact area in the ankle joint using a Tekscan sensor, rotation of the talus and calcaneus, and translation of the calcaneus using a three-dimensional motion capture system. Ankles then underwent sectioning of the ATFL and CFL (injured), retested, then randomly assigned to ATFL-only Broström repair or combined ATFL and CFL repair. Testing was repeated after repair then loaded in inversion to failure (LTF). RESULTS: The stiffness of the ankle was not significantly increased compared to the injured condition by repairing the ATFL only (n.s.) or the ATFL/CFL (n.s.). The calcaneus had significantly more rotation than the injured condition in the ATFL-only repair (p = 0.037) but not in the ATFL/CFL repair (n.s.). The ATFL failed at 40.3% higher torque than the CFL, at 17.4 ± 7.0 N m and 12.4 ± 4.1 N m, respectively, and 62.0% more rotation, at 43.9 ± 5.6° and 27.1 ± 6.8°, respectively. CONCLUSIONS: There was a greater increase in stiffness following combined ATFL/CFL repair compared to ATFL-only repair, although this did not reach statistical significance. The CFL fails before the ATFL, potentially indicating its vulnerability immediately following repair. LEVEL OF EVIDENCE: III, case-control therapeutic study.

Precontoured Quadrilateral Surface Acetabular Plate Fixation Demonstrates Increased Stability When Compared With Pelvic Reconstruction Plates: A Biomechanical Study.

OBJECTIVE: To compare the stability of 3 fixation strategies for a transverse acetabular fracture: a reconstruction plate with anterior and posterior column screws (group A); an infrapectineal precontoured quadrilateral surface buttress (iPQSB) plate alone (group B); and an anterior column lag-screw and iPQSB plate (group C). METHODS: A transverse acetabular fracture was created in 18 synthetic hemipelvises. Six were fixed by each of the 3 methods described. Specimens underwent cyclic axial compressive loading to 1700N for 42,000 cycles while anterior and posterior column displacements were measured, followed 4800N for 50 cycles. Displacement and stiffness data were analyzed with analysis of variance and Tukey HSD. A Cox proportional hazards regression model was used to determine survival rate. P values < 0.05 were considered significant. RESULTS: Group C had significantly less posterior column displacement (0.16 ± 0.06 mm) compared with group B (0.38 ± 0.37 mm, P < 0.0001) and group A (0.38 ± 0.37 mm, P < 0.0001). In addition, group A had significantly more anterior column displacement (0.28 ± 0.11 mm) than group B (0.22 ± 0.14 mm, P = 0.0310) and group C (0.18 ± 0.09 mm, P = 0.0001). Group C was 10.5% stiffer than group A (P = 0.0037). Group B had a 7.27x greater rate of failure than group C (95% confidence interval, 1.6-33.2). DISCUSSION AND CONCLUSION: Under anatomical loading, iPQSB plates with anterior column lag-screw fixation demonstrate increased stability in a synthetic bone transverse acetabular fracture model. Based on our data, we support additional evaluation of early weight-bearing after transverse acetabular fracture fixation in patients with healthy bone when an anterior column screw-iPQSB plate construct is used.

The Role of Complete Posterior Cruciate Ligament Release in Flexion Gap Balancing for Total Knee Arthroplasty.

BACKGROUND: The sequence of posterior cruciate ligament (PCL) release in posterior-substituting designs, when performing gap balancing in total knee arthroplasty (TKA), is variable. We hypothesize that early complete PCL release during knee exposure will change the flexion balance to result in a uniform medial-lateral flexion gap symmetry at the time of implant placement. METHODS: Ten cadaveric knees were prepared for TKA using standard medial parapatellar approach. Medial and lateral flexion gaps were measured in the conditions of intact, partial (50%) resection, and full resection of PCL. Measurements were performed with both surgical navigation and a caliper. Flexion gap distances were reported for medial and lateral compartments in the 3 PCL conditions. RESULTS: Medial flexion gap increased after only complete release of the PCL (mean 3.94-5.05 mm). The lateral flexion gap increased as well (mean 4.17-4.67 mm). Complete PCL release resulted in a statistically significant increase in medial flexion gap compared to intact (P = .013) and partially released (P = .012) specimens. No significant differences were noted in lateral flexion gap change. Notable change in medial versus lateral gap (flexion gap symmetry) relationship occurred after just partial PCL release (P = .018). CONCLUSION: Among the 3 PCL states, changes in flexion gap distance were most conspicuous in the medial compartment. This suggests gap balancing performed with incomplete PCL release will not accurately reflect gap distance after eventual PCL removal, thus supporting the hypothesis. It is recommended that the PCL should be released to the fullest extent possible before ligament tensioning for femoral component rotation in posterior-stabilized TKA.

A New Fastener With Improved Bone-To-Implant Interface Shows Superior Torque Stripping Resistance Compared With the Standard Buttress Screw.

OBJECTIVE: The conventional AO buttress screw used for fracture fixation relies on a historic buttress thread design, which is prone to stripping at the bone-implant interface. We hypothesized that a new Bone-Screw-Fastener with an innovative interlocking thread design demonstrates increased resistance to torque stripping forces compared with the buttress screw, without compromising pullout strength. METHODS: A biomechanical model was established in 6 matched pairs of adult human cadaveric tibiae to test torque resistance between the 3.5 mm Bone-Screw-Fastener and the 3.5 mm cortical AO buttress screw until failure. Uniaxial pullout testing of both screw types was performed as an internal control experiment. RESULTS: The 3.5 mm Bone-Screw-Fastener had a significantly increased resistance to torque failure compared with the standard 3.5 mm AO buttress screw (P = 0.0145). In contrast to the buttress screws, none of the Bone-Screw-Fasteners stripped from the bone but rather failed at the screwdriver-implant interface in terms of a metal-on-metal failure. The internal control experiments revealed no significant difference in axial pullout strength between the 2 implants (P = 0.47). CONCLUSIONS: These data demonstrate the superiority of the new Bone-Screw-Fastener over the conventional AO buttress screw regarding protection from torque stripping forces. In addition, the new thread design that interlocks to the bone does not sacrifice axial pullout resistance conveyed by the buttress screw. Future controlled trials will have to validate the in vivo relevance of these findings in a clinical setting.

Biomechanical Comparison of Low-Profile Contoured Locking Plate With Single Compression Screw to Fully Threaded Compression Screws for First MTP Fusion.

BACKGROUND: Open metatarsophalangeal (MTP) arthrodesis using locked plates produces good clinical outcomes. However, arthroscopic fusion with new-generation fully threaded compression screws is emerging as an alternative. The purpose of this study was to compare low-profile contoured locked plates with fully threaded compression screws for first MTP fusion, in a biomechanical cadaveric model. METHODS: The first rays of 8 matched pairs of fresh frozen cadaveric feet underwent dissection and dual-energy x-ray absorptiometry (DEXA) scanning to measure bone mineral density (BMD). The "plate" group was prepared with cup-and-cone reamers, and fixation of the MTP joint with 1 compression screw and low-profile dorsal locked plate. The matched-pair "screws" group was prepared through a simulated arthroscopic technique, achieving fixation with 2 new-generation fully threaded compression screws. The plantar MTP gap was recorded with an extensometer during 250 000 90-N cyclic loads followed by a single load to failure. RESULTS: The screw group demonstrated significantly greater stiffness, 31.6 N/mm (plates) and 51.7 N/mm (screws) (P = .0045). There was no significant difference in plantar gapping or load to failure, 198.6 N (plates) and 290.1 N (screws) (P = .2226). Stiffness and load to failure were highly correlated to BMD for the screw group, r =0.79 and r = 0.94, respectively, but less so for the plate group, r = 0.36 and r = 0.62, respectively. The maximum metatarsal head height measured on the lateral view was strongly correlated with load to failure for both the plate- and screw-only groups (r > 0.9). CONCLUSION: These data demonstrate that hallux MTP arthrodesis utilizing fully threaded compression screws had similar plantar gapping and load to failure when compared with the low-profile locking plate, but with significantly more stiffness. These results support an increased role of fully threaded screws for MTP arthrodesis using either the arthroscopic or open technique. However, with decreased BMD plate fixation may remain the better fixation choice. CLINICAL RELEVANCE: Our data suggest that with regard to construct stability, fully threaded headless compression screws may be just as effective as low-profile locking plates, but BMD and MTP joint fluoroscopic measurements should be considered in the decision-making process for fixation.

The Role of Calcaneofibular Ligament Injury in Ankle Instability: Implications for Surgical Management.

BACKGROUND: Acute inversion ankle sprains are among the most common musculoskeletal injuries. Higher grade sprains, including anterior talofibular ligament (ATFL) and calcaneofibular ligament (CFL) injury, can be particularly challenging. The precise effect of CFL injury on ankle instability is unclear. HYPOTHESIS: CFL injury will result in decreased stiffness, decreased peak torque, and increased talar and calcaneal motion and will alter ankle contact mechanics when compared with the uninjured ankle and the ATFL-only injured ankle in a cadaveric model. STUDY DESIGN: Descriptive laboratory study. METHODS: Ten matched pairs of cadaver specimens with a pressure sensor in the ankle joint and motion trackers on the fibula, talus, and calcaneus were mounted on a material testing system with 20° of ankle plantarflexion and 15° of internal rotation. Intact specimens were axially loaded to body weight and then underwent inversion along the anatomic axis of the ankle from 0° to 20°. The ATFL and CFL were sequentially sectioned and underwent inversion testing for each condition. Linear mixed models were used to determine significance for stiffness, peak torque, peak pressure, contact area, and inversion angles of the talus and calcaneus relative to the fibula across the 3 conditions. RESULTS: Stiffness and peak torque did not significantly decrease after sectioning of the ATFL but decreased significantly after sectioning of the CFL. Peak pressures in the tibiotalar joint decreased and mean contact area increased significantly after CFL release. Significantly more inversion of the talus and calcaneus as well as calcaneal medial displacement was seen with weightbearing inversion after sectioning of the CFL. CONCLUSION: The CFL contributes considerably to lateral ankle instability. Higher grade sprains that include CFL injury result in significant decreases in rotation stiffness and peak torque, substantial alteration of contact mechanics at the ankle joint, increased inversion of the talus and calcaneus, and increased medial displacement of the calcaneus. CLINICAL RELEVANCE: Repair of an injured CFL should be considered during lateral ligament reconstruction, and there may be a role for early repair in high-grade injuries to avoid intermediate and long-term consequences of a loose or incompetent CFL.

Gravity Fluid Flow More Accurately Reflects Joint Fluid Pressure Compared With Commercial Peristaltic Pump Systems in a Cadaveric Model.

PURPOSE: To evaluate intra-articular fluid pressures and joint compliance generated by fluid management systems on cadaveric shoulders and knees under simulated arthroscopic conditions, and to compare joint compliance between knee and shoulder specimens. METHODS: Intra-articular pressures of 5 cadaver shoulders and 5 knees were recorded for 4 arthroscopic pumps (Stryker FloControl, Stryker CrossFlow, Arthrex DualWave, DePuy Mitek FMS Duo) and a gravity feed system. Each specimen was tested 6 times with a pressure transducer for 2 minutes at 0, 25%, and 50% suction. The average pressures were analyzed with 1-way analysis of variance and Tukey's honestly significant difference tests (P < .05). RESULTS: At all suction levels, all pumps exhibited significantly greater pressure than gravity feed (P = .001 to P < .001). At both 25% and 50% suction, FloControl displayed significantly greater pressures (Pmax 160.44 mm Hg) than the other pumps or gravity feed (Pmax 46.9 mm Hg). CrossFlow had the lowest net percentage error (36.8%, 18.4 mm Hg) when compared with the standard pressure of 50 mm Hg, followed by gravity feed. All pumps had large initial overshoot (ie, Pinitial CrossFlow 99.4 mm Hg) followed by settling time, whereas gravity feed did not (Pinitial 55.2 mm Hg). CONCLUSIONS: Gravity feed is an accurate, reliable delivery method for arthroscopic fluid with minimal overshoot and lower intra-articular pressure ranges than commercial pump systems. There was no evidence of plastic deformation of the joint capsule, because capsular compliance increased linearly in both knee and shoulder specimens throughout testing within the established safe range of intra-articular pressures. CLINICAL RELEVANCE: Arthroscopic flow management systems produce maximal and overshoot pressures that are not seen with gravity flow. Surgeons should understand intra-articular pressure and fluid delivery behavior during shoulder and knee arthroscopy to adapt to the variability and higher maximal pressures when using pump systems. Maintaining appropriate pressure could prevent fluid extravasation and possible neuromuscular dysfunction.