Contributions of capsular releases to femoral exposure in total hip arthroplasty via the direct anterior approach.

BACKGROUND: In total hip arthroplasty via the direct anterior approach, appropriate exposure is critical to allow preparation of the femur. The objective of this study was to explore the optimal soft tissue releases needed to allow broaching of the femur through a combination of experimental tests and computer simulations. METHODS: Fourteen full-body cadaveric specimens were included in this study. Total hip arthroplasty was performed via the direct anterior approach with the femur at 20° adduction and 20°extension. Soft tissue releases were performed sequentially, namely, the transverse iliofemoral ligament, descending iliofemoral ligament, ischio-femoral ligament, conjoint tendon, and obturator externus. After each release, the femur mobility was assessed by applying a 6 Nm external rotation torque and a 120 N distraction force. Subsequently, using specimen-specific models and models of the broach and handle, the broach passage after each release was simulated, and the release that allowed broach passage was analyzed. FINDINGS: The average external rotation after releasing the transverse and descending iliofemoral ligaments increased by 14.1° ± 6.1° and 13.8° ± 5.3°. With subsequent soft tissue releases, the rotational mobility increased incrementally, though the impact decreased. Impingement between the broach passage and the pelvis was mainly at the anterior superior iliac spine and the anterior inferior iliac spine. The volume of impingement decreased from 4.8 ± 4.5 cm3 after resection of the femoral head to 1.8 ± 1.6 cm3 and 1.2 ± 1.9 cm3 after release of the transverse and descending iliofemoral ligament, respectively. INTERPRETATION: With sequential soft-tissue releases, the femur mobility increased incrementally. However, the number of releases needed for each femur varied extensively between specimens. Most (10/14) femurs became accessible after the release of the ilio-femoral or ischio-femoral ligament.

Single-Strand "Short Isometric Construct" Medial Collateral Ligament Reconstruction Restores Valgus and Rotational Stability While Isolated Deep MCL and Superficial MCL Reconstruction Do Not.

BACKGROUND: Historical MCL (medial collateral ligament) reconstruction (MCLR) techniques have focused on the superficial MCL (sMCL) to restore valgus stability while frequently ignoring the importance of the deep MCL (dMCL) in controlling tibial external rotation. The recent recognition of the medial ligament complex importance has multiple studies revisiting medial anatomy and questioning contemporary MCLR techniques. PURPOSE: To assess whether (1) an isolated sMCL reconstruction (sMCLR), (2) an isolated dMCL reconstruction (dMCLR), or (3) a novel single-strand short isometric construct (SIC) would restore translational and rotational stability to a knee with a dMCL and sMCL injury. STUDY DESIGN: Controlled laboratory study. METHODS: Biomechanical testing was performed on 14 fresh-frozen cadaveric knee specimens using a custom multiaxial knee activity simulator. The specimens were divided into 2 groups. The first group was tested in 4 states: intact, after sectioning the sMCL and dMCL, isolated sMCLR, and isolated dMCLR. The second group was tested in 3 states: intact, after sectioning the sMCL and dMCL, and after single-strand SIC reconstruction (SICR). In each state, 4 loading conditions were applied at 0°, 20°, 40°, 60°, and 90° of knee flexion: 8-N·m valgus torque, 5-N·m external rotation torque, 90-N anterior drawer, and combined 90-N anterior drawer plus 5-N·m tibial external rotation torque. Anterior translation, valgus rotation, and external rotation of the knee were measured for each state and loading condition using an optical motion capture system. RESULTS: sMCL and dMCL transection resulted in increased laxity for all loading conditions at all flexion angles. Isolated dMCLR restored external rotation stability to intact levels throughout all degrees of flexion, yet valgus stability was restored only at 0° of flexion. Isolated sMCLR restored valgus and external rotation stability at 0°, 20°, and 40° of flexion but not at 60° or 90° of flexion. Single-strand SICR restored valgus and external rotation stability at all flexion angles. In the combined anterior drawer plus external rotation test, isolated dMCL and single-strand SICR restored stability to the intact level at all flexion angles, while the isolated sMCL restored stability at 20° and 40° of flexion but not at 60° or 90° of flexion. CONCLUSION: In the cadaveric model, single-strand SICR restored valgus and rotational stability throughout the range of motion. dMCLR restored rotational stability to the knee throughout the range of motion but did not restore valgus stability. Isolated sMCLR restored external rotation and valgus stability in early flexion. CLINICAL RELEVANCE: In patients with anteromedial rotatory instability in the knee, neither an sMCLR nor a dMCLR is sufficient to restore stability.

Pelvic tilt affects superolateral coverage, but not superomedial coverage of the femoral head following periacetabular osteotomy.

BACKGROUND: Pelvic tilt is an important sagittal parameter that varies greatly among individuals. The objective of this study was to quantify the effect of pelvic tilt on femoral head coverage and range of motion in a dysplastic population following periacetabular osteotomy. METHODS: Twenty-three dysplastic hips from 19 patients (17 female, 2 male) were included in this study. Three-dimensional models were reconstructed using pre-operative CT images, and patient-specific neutral pelvic tilt was obtained on an anteroposterior X-ray. Following a simulated periacetabular osteotomy, the pelvic tilt was changed from -15° to +15°, and the effects on femoral head coverage and hip range of motion was quantified using a customized MATLAB program. FINDINGS: Pelvic tilt did not significantly affect total femoral head coverage (P > 0.2). However, a 15° anterior tilt from neutral resulted in a 17.72 ± 9.45% increase in anterolateral coverage and a 23.96 ± 7.48% decrease in posterolateral coverage (P < 0.0001), as well as an 18.2 ± 8.4° loss of internal rotation at 90° of hip flexion. Contrarily, posterior pelvic tilt led to a 26.79 ± 9.04% reduction in anterolateral coverage (P < 0.0001) and an 18.02 ± 9.57% increase in posterolateral coverage (P < 0.0001), and the maximum internal rotation increased 11.8 ± 3.7°. INTERPRETATION: While pelvic tilt did not affect total femoral head coverage, it had a significant impact on the distribution of coverage within the superolateral region of the femoral head. Anterior pelvic tilt led to increased anterolateral coverage, but also had a negative impact on hip range of motion. An optimal surgical plan should achieve adequate coverage while not significantly limiting the patient's mobility.

Variations in Trochlear Morphology of Contemporary and Legacy Total Knee Arthroplasty Prostheses: A Review of 22 Designs.

BACKGROUND: The morphology of the trochlear compartment of total knee arthroplasty (TKA) prostheses is a major determinant of postoperative patello-femoral kinematics, particularly with unresurfaced patellae. The objective of this study was to quantify and compare the trochlear morphology of a large series of contemporary and legacy TKA designs. METHODS: The 3-dimensional surface models of 22 femoral components (13 contemporary and 9 legacy) were created using high-resolution laser scanning. The trochlear profile of each component was analyzed from proximal to distal in 15° increments around the trochlear axis. In each profile, the following variables were measured: sulcus angle, medio-lateral deviation of the sulcus, the height and width of the facets, and the trochlear groove orientation. RESULTS: In the contemporary group, the sulcus angle decreased progressively along the trochlear arc to varying degrees, except for 2 symmetrical designs, whereas the sulcus angle of the legacy designs showed considerable variability. The height of the medial facet was very strongly correlated with that of the lateral facet in the contemporary group (R2 = 0.89), whereas the correlation was weak for the legacy designs (R2 = 0.36). Moreover, the trochlear sulcus deviated laterally from distal to proximal in 10 contemporary designs and 7 legacy designs, resulting in a trochlear groove orientation of 4.2 to 11.1° and 4.3 to 10.5°, respectively. In the remaining 5 designs (3 contemporary and 2 legacy), the sulcus was vertical. CONCLUSIONS: There is more consistency in trochlear morphology of contemporary TKA designs compared to that of legacy designs, yet there are still large variations between different designs.

The Stability of Fixation of Vancouver B2 Periprosthetic Femoral Fractures: Effect of Implantation Technique.

BACKGROUND: Due to increasing volume of total hip arthroplasties, periprosthetic femoral fractures have become a common complication with increased revision burden and perioperative morbidity. The objective of this study was to evaluate the fixation stability of Vancouver B2 fractures treated with 2 techniques. METHODS: A common B2 fracture was created by reviewing 30 type B2 cases. The fracture was then reproduced in 7 pairs of cadaveric femora. The specimens were divided into 2 groups. In Group I ("reduce-first"), the fragments were reduced first, followed by implantation of a tapered fluted stem. In Group II ("ream-first"), the stem was implanted in the distal femur first, followed by fragment reduction and fixation. Each specimen was loaded in a multiaxial testing frame with 70% of peak load during walking. A motion capture system was used to track the motion of the stem and fragments. RESULTS: The average stem diameter in Group II was 16.1 ± 0.4 mm, versus 15.4 ± 0.5 mm in Group I. The fixation stability was not significantly different in the 2 groups. After the testing, the average stem subsidence was 0.36 ± 0.31 mm and 0.19 ± 0.14 mm (P = .17) and the average rotation was 1.67 ± 1.30° and 0.91 ± 1.11° (P = .16) in Groups I and II, respectively. Compared to the stem, there was less motion of the fragments and there was no difference between the 2 groups (P > .05). CONCLUSIONS: When tapered fluted stems were used in combination with cerclage cables for treatment of Vancouver type B2 periprosthetic femoral fractures, both the "reduce-first" and "ream-first" techniques showed adequate stem and fracture stability.

The Length of Diaphyseal Contact of Tapered Fluted Stems is Highly Dependent on Canal Morphology.

BACKGROUND: Diaphyseal fixation remains the mainstay of revision THA. The stability of diaphyseal fixation can be quantified by the extent of contact between the stem and the endosteal cortex. This is highly affected by the morphology of the proximal femur. The purpose of this study was to examine factors affecting diaphyseal contact in the revision THA and to identify preoperative predictors of adequate fixation. METHODS: Three-dimensional femur models were created from CT scans of 33 Dorr B and C femora. The proximal 120 mm of the femur was omitted to mimic proximal bone deficiency. A tapered fluted stem (3 degrees, 150 mm) model was virtually implanted after reaming of the medullary canal. The contact length between stem and endosteal cortex was measured, in addition to other variables. The relationship between variables was evaluated using Spearman's correlation, and logistic regression analysis was used to identify predictors of the contact length (P < .05). RESULTS: The contact length varied widely between specimens (66.5 ± 16.6 mm, range: 21-98 mm). Contact increased with the depth of the isthmus below the lesser trochanter (range: 55-155 mm; r2 = 0.473, P = .005) and the distance between the isthmus and the distal edge of the damage zone (range: -9 to 96 mm; r2 = 0.508, P = .002). Stepwise regression identified the reaming length, distance between fracture and the isthmus, and isthmus diameter as independent predictors of contact length (r = 0.643). CONCLUSIONS: Contact is limited in specimens where the isthmus is more proximally located. In these cases, supplementary fixation using plating and/or longer, curved prosthesis may be considered.

Micromotion and Migration of Cementless Tibial Trays Under Functional Loading Conditions.

BACKGROUND: The outcome of cementless total knee arthroplasty (TKA) relies on successful bony ingrowth into the implant surfaces. Failures due to aseptic loosening are still reported, especially in younger and more active patients. The objective of this study is to quantify the micromotion of a commercially available design of cementless tibial tray under loading conditions simulating walking and stair descent. METHOD: A commercially available design of cementless total knee arthroplasty was implanted in 7 cadaveric knees which were preconditioned with 500 cycles of 0°-100° flexion under a vertical load of 1050 N in a custom-built, multiaxial functional activity simulator. This was followed by application of the peak forces and moments occurring during walking and stair descent. During each loading procedure, 3-dimensional motion at the bone-prosthesis interface was measured using digital image correlation. RESULTS: The tray migrated 101 ± 25 µm on average during preconditioning, which was dominated by rotation in the sagittal plane (92% of total migration), combined with posterior translation (28%) and minimal rotation in the transverse plane (14%). The migration varied 2.7-fold (61-167 µm) between the 6 measurement zones. Stair descent produced significantly higher total micromotion than walking in zone #5 (62 ± 9 vs 51 ± 10 µm, P < .05) and zone #6 (68 ± 17 vs 37 ± 10 µm, P < .05). In addition, during stair descent, the tray exhibited significantly more tilting (anterior zones: 31 ± 17 vs -16 ± 20 µm, P < .05; posterior zones: -60 ± 8 vs -40 ± 7 µm, P < .05) and more anteroposterior displacement in the anterior zones (-25 ± 3 vs -13 ± 2 µm, P < .05) when compared to walking. CONCLUSION: The relative motion at the bone-prosthesis interface varied substantially around the periphery of the cementless tray. Under the loading conditions evaluated, the tray primarily underwent a rocking motion in the sagittal plane. Compared with walking, stair descent produced significantly more micromotion, especially in the posterior zones.

The continuum of hip range of motion: From soft-tissue restriction to bony impingement.

Traditional studies of hip kinematics have not identified which anatomic structures limit the range of motion (ROM) when the hip is placed in different maneuvers. In this study, we attempted to answer two questions: (a) During which maneuvers is the motion of the hip limited by bony impingement between the femur and pelvis? (b) When is hip ROM determined by the constraint of soft tissues and to what extent? ROM of eight cadaveric hips was measured in 17 maneuvers using a motion capture system. The maneuvers were recreated in silico using 3D CT models of each specimen to detect the occurrence of bony impingement. If bony impingement was not detected, the variable component of 3D hip motion was increased until a collision was detected. The difference between the virtual ROM at the point of bony impingement and the initial ROM measured experimentally was termed as the soft-tissue restriction. The results showed that bony impingement was present in normal hips during maneuvers consisting of high abduction with flexion, and high flexion combined with adduction and internal rotation. At impingement-free maneuvers, the degree of soft tissue restriction varies remarkably, ranging from 4.9° ± 3.8° (internal rotation) at 90° of flexion to 80.0° ± 12.5° (internal rotation) at maximum extension. The findings shed light on the relative contributions of osseous and soft tissues to the motion of the hip in different maneuvers and allow for a better understanding of physical exams of different purposes in diagnosing bone- or soft tissue-related diseases.

How Flat Is the Tibial Osteotomy in Total Knee Arthroplasty?

BACKGROUND: Cementless total knee arthroplasty has been developed to decrease the incidence of failure in younger and more active patients. However, failures are still more common in cementless versus cemented components. It is hypothesized that this is triggered by incomplete bone-tray contact. The present study compares the final contact area of a cementless tray as a function of the initial osteotomy flatness. METHODS: Eight surgeons prepared 14 cadaveric knees for cementless total knee replacement using standard instrumentation. The topography of each osteotomy was captured with a laser scanner; 3-dimensional computer models of the surfaces were generated. After scanning each tibia, the surgeons implanted cementless tibial trays using a manual impactor. Each tibia was then dissected, embedded in mounting resin, and sectioned. The sectioned blocks were observed under stereomicroscopy to identify points of bone-tray contact which were incorporated into the 3-dimensional models. Maps were then generated illustrating depicting contacting and noncontacting areas. RESULTS: The mean initial flatness of all specimens was 1.1 ± 0.35 mm. After impaction, 79.4% ± 0.3% of the surface had established bony contact. Of the noncontacting areas, 17.6% were within 0.3 mm of the tray. Only 2.6% of the surface was at distances reported to impede ingrowth. Noncontacting areas were typically located centrally. A trend in decreasing percent contact area with increased flatness tolerance was observed (R2 = 0.605). CONCLUSION: (1) There is an inverse correlation between the flatness of the tibial osteotomy and the percentage of the bony surface in contact with underside of the tibial tray. (2) Almost all tray-tibia contact is generated during implantation through flattening of elevated features on the tibial surface. (3) Gaps between the tray and the tibia are consistently located in the central regions of the osteotomy proximal to the medullary canal.

Hypothermia in Total Joint Arthroplasty: A Wake-Up Call.

BACKGROUND: Total joint patients are particularly vulnerable to perioperative hypothermia (PH) (combined effects of anesthesia, radiation, and convective heat loss from exposed skin surfaces and cool temperatures in the operating room). There are limited studies on PH in these patients. METHODS: In a retrospective review of 204 patients undergoing primary hip and 179 undergoing primary knee replacement surgeries, time and temperature parameters were collected from the electronic health records from preoperative and postoperative recovery room nursing assessments, intraoperative anesthesia records, and floor nursing notes. Basic patient demographic data was recorded. Chi-squared and paired t-tests were used to compare between hypothermic and normothermic groups. RESULTS: At the time of incision, 60 of 179 (34%) total knee arthroplasty (TKA) patients and 80 of 204 (39%) total hip arthroplasty (THA) patients were hypothermic. In THA patients, 65% remained hypothermic for the duration of anesthesia compared to 33% of TKA patients. The largest drop in core body temperature in both THA and TKA patients occurred between preoperative holding and induction of anesthesia. In THA patients, spinal anesthesia had a significantly higher occurrence of PH. No significant patient factor was found to increase risk. CONCLUSION: Emphasis on preoperative holding protocols, decreasing time from operating room entry to incision, and increasing ambient room temperature could reduce risk of hypothermia in total joint replacement patients.

How Does Level and Type of Experience Affect Measurement of Joint Range of Motion?

OBJECTIVES: Comparison of range of motion measurements by 3 types of investigators with different levels and types of training using three different measurement techniques. The study hypothesis was that the accuracy and precision of range of motion measurements would vary based on (1) the level and type of experience of the investigator and (2) the measurement technique used. DESIGN/SETTING: Descriptive laboratory study. PARTICIPANTS: Ten fresh frozen cadavers (20 upper and 20 lower extremities). INTERVENTIONS: Shoulder, elbow, hip, and knee motion were measured using 3 different measurement techniques (digital photography, goniometry, and visual estimation) by 3 groups of investigators (attending orthopedic surgeons, physical therapists, and residents). Accuracy was defined by the difference from the reference standard (motion capture analysis), whereas precision was defined by the proportion of measurements within either 5° or 10° of the reference standard. Analysis of variance, t-tests, and chi-squared tests were used. RESULTS: Statistically significant (p < 0.05) differences in accuracy were found for hip flexion, abduction, internal rotation, external rotation, and knee flexion. However, none of these differences met the authors' defined clinical significance (maximum difference 3°). Precision was significantly (p < 0.05) different for elbow extension, hip flexion, abduction, internal rotation, external rotation, and knee flexion. CONCLUSION: This study found that clinically accurate measurements of shoulder, elbow, hip, and knee motion are obtained regardless of technique used or the investigators' level and type of experience. Precision was equivalent for all shoulder motions, elbow flexion, and knee extension, but varied by as much as 7% to 28% between groups for all other motions.

Is digital photography an accurate and precise method for measuring range of motion of the shoulder and elbow?

BACKGROUND: Accurate measurements of shoulder and elbow motion are required for the management of musculoskeletal pathology. The purpose of this investigation was to compare three techniques for measuring motion. The authors hypothesized that digital photography would be equivalent in accuracy and show higher precision compared to the other two techniques. METHODS: Using infrared motion capture analysis as the reference standard, shoulder flexion/abduction/internal rotation/external rotation and elbow flexion/extension were measured using visual estimation, goniometry, and digital photography on 10 fresh frozen cadavers. These measurements were performed by three physical therapists and three orthopaedic surgeons. Accuracy was defined by the difference from the reference standard (motion capture analysis), while precision was defined by the proportion of measurements within the authors' definition of clinical significance (10° for all motions except for elbow extension where 5° was used). Analysis of variance (ANOVA), t-tests, and chi-squared tests were used. RESULTS: Although statistically significant differences were found in measurement accuracy between the three techniques, none of these differences met the authors' definition of clinical significance. Precision of the measurements was significantly higher for both digital photography (shoulder abduction [93% vs. 74%, p < 0.001], shoulder internal rotation [97% vs. 83%, p = 0.001], and elbow flexion [93% vs. 65%, p < 0.001]) and goniometry (shoulder abduction [92% vs. 74%, p < 0.001] and shoulder internal rotation [94% vs. 83%, p = 0.008]) than visual estimation. Digital photography was more precise than goniometry for measurements of elbow flexion only [93% vs. 76%, p < 0.001]. CONCLUSIONS: There was no clinically significant difference in measurement accuracy between the three techniques for shoulder and elbow motion. Digital photography showed higher measurement precision compared to visual estimation for shoulder abduction, shoulder internal rotation, and elbow flexion. However, digital photography was only more precise than goniometry for measurements of elbow flexion. Overall digital photography shows equivalent accuracy to visual estimation and goniometry, but with higher precision than visual estimation.

Is digital photography an accurate and precise method for measuring range of motion of the hip and knee?

BACKGROUND: Accurate measurements of knee and hip motion are required for management of musculoskeletal pathology. The purpose of this investigation was to compare three techniques for measuring motion at the hip and knee. The authors hypothesized that digital photography would be equivalent in accuracy and show higher precision compared to the other two techniques. METHODS: Using infrared motion capture analysis as the reference standard, hip flexion/abduction/internal rotation/external rotation and knee flexion/extension were measured using visual estimation, goniometry, and photography on 10 fresh frozen cadavers. These measurements were performed by three physical therapists and three orthopaedic surgeons. Accuracy was defined by the difference from the reference standard, while precision was defined by the proportion of measurements within either 5° or 10°. Analysis of variance (ANOVA), t-tests, and chi-squared tests were used. RESULTS: Although two statistically significant differences were found in measurement accuracy between the three techniques, neither of these differences met clinical significance (difference of 1.4° for hip abduction and 1.7° for the knee extension). Precision of measurements was significantly higher for digital photography than: (i) visual estimation for hip abduction and knee extension, and (ii) goniometry for knee extension only. CONCLUSIONS: There was no clinically significant difference in measurement accuracy between the three techniques for hip and knee motion. Digital photography only showed higher precision for two joint motions (hip abduction and knee extension). Overall digital photography shows equivalent accuracy and near-equivalent precision to visual estimation and goniometry.

Will New Metal Heads Restore Mechanical Integrity of Corroded Trunnions?

BACKGROUND: Metal wear and corrosion from modular junctions in total hip arthroplasty can lead to further unwanted surgery. Trunnion tribocorrosion is recognized as an important contributor to failure. This study was performed to determine if new metal heads restore mechanical integrity of the original modular junction after impaction on corroded trunnions, and assess which variables affect stability of the new interface created at revision total hip arthroplasty. METHODS: Twenty-two trunnions, cobalt-chromium (CoCr) and titanium alloy (TiAIV), (CoCr, n = 12; TiAIV, n = 10) and new metal heads were used, 10 trunnions in pristine condition and 12 with corrosion damage. Test states were performed using an MTS Machine and included the following: 1, Assembly; 2, Disassembly; 3, Assembly; 4, Toggling; and 5, Disassembly. During loading, three-dimensional motion of the head-trunnion junction was measured using a custom jig. RESULTS: There were no statistical differences in the tested mechanical properties between corroded and pristine trunnions implanted with a new metal femoral head. Average micromotion of the head versus trunnion interface was greatest at the start of loading, stabilizing after approximately 50 loading cycles at an average of 30.6 ± 3.2 µm. CONCLUSION: Corrosion at the trunnion does not disrupt mechanical integrity of the junction when a CoCr head is replaced with a CoCr trunnion. However, increased interface motion of a new metal head on a corroded titanium trunnion requires additional study. The evaluation of ball head size on mechanical integrity of trunnions would also be a potential subject of future investigation, as increasing the ball head size at the time of revision is not uncommon in revisions today.

Stemmed tibial revision component alignment: Does an anatomic conflict exist?

INTRODUCTION: Obtaining satisfactory coronal plane alignment is important for success in revision total knee arthroplasty (TKA). The study objective was to determine tibial coronal plane alignment after TKA when a tibial stem was used and assess if there was an anatomic conflict in tibial stemmed component alignment. MATERIALS AND METHODS: A radiographic review of 88 revision TKA cases was performed. Full length leg radiographs were examined for varus/valgus alignment, defined as greater than or equal to three degrees from neutral 180 degrees, canal or non-canal filling tibial stems, and any native tibial bow. RESULTS: In tibias with a native valgus alignment of three or more degrees, a canal-filling stem allowed little flexibility to improve final positioning of the tibial stem and resulted in a valgus alignment of the tibial stem in 87.5% of cases, where a canal filling stem was utilized. A non-canal filling stem utilized in native valgus tibias allowed on average a two-degree improvement in tibial alignment and 64.7% of cases resulted in a neutral placement of the tibial stem. CONCLUSION: Implanting the tibial component in a desired position is limited by type of stem and the native angulation of the tibia. When anatomic conflict exists between tibial mechanical axis and the intramedullary canal, canal filling stems may compromise coronal alignment.

Quantifying and Predicting Surgeon Work Effort for Primary and Revision Total Knee Arthroplasty.

BACKGROUND: The objectives of this study were to quantify increased utilization of resources in revision total knee arthroplasty (TKA) compared with primary TKA, determine preoperative factors that predict outcome measures, and compare Medicare reimbursement for each procedure. METHODS: Seventy-eight revision TKA patients were compared with 80 primary TKA patients. Outcomes measured were surgical time, estimated blood loss, length of stay, and complications. RESULTS: Revision TKA showed 49% increased surgical time compared with primary TKA. Estimated blood loss was increased 91%. Tibial and femoral bone loss was associated with increased surgical time as was use of longer stemmed tibial components. Average Medicare hospital payment increased 29% ($13,464 for primary, $17,331 for revision). Average physician reimbursement represented a 36% increase. Relative value units were increased to 31%. CONCLUSION: There was substantial increase in work effort not commensurate with current Medicare reimbursement, which may limit patient access to revision TKA.

Quantifying and Predicting Surgeon Work Input in Primary vs Revision Total Hip Arthroplasty.

BACKGROUND: Primary total hip arthroplasties (THAs) performed annually are projected to increase 174% by 2030, causing a parallel increase for revision THA. Increased surgical effort and readmission rates associated with revision THA may discourage surgeons from performing them. Although revision THA Medicare reimbursement is greater, it may be disproportionate to time and effort. We examined work input between primary and revision THA, assessing predictive factors. We also compared surgeon work input to current reimbursement. METHODS: A total of 156 patients were identified, 80 primary and 76 revision THA. Demographic, clinical, and radiographic data were collected. Radiographic data were collected from the most recent preoperative radiographs taken before primary or revision THA. Multiple linear and logistic regression models were used to identify patient factors contributing to select outcome variables by a stepwise method, with a probability value for entry (P = .05) and removal (P = .10). Residual analysis was performed, confirming validity of these models. RESULTS: Average age, body mass index, and percentage of female patients were similar between cohorts. There was no statistically significant difference between the demographic variables, although data revealed patient variables contributing to statistically significant increases in surgical time, length of stay, blood loss, and complications with revision THA. CONCLUSION: Despite a 66% increase in "percent effort" and 3-fold higher readmission rate, revision THA requires at least a 2-fold increase because of nonquantifiable factors. Revision THA demonstrates a substantial increase in work effort not commensurate with current Medicare reimbursement, which may force surgeons to limit or eliminate revision arthroplasties performed reducing access to patient care.

Wear Patterns in Knee Articular Surfaces in Varus Deformity.

This study was performed to study the relationship between the degree of varus deformity of osteoarthritic knees and the anatomic distribution of cartilage pathology. Bone wafers resected from the distal femur and proximal tibia were obtained from 107 patients (195 knees) with primary varus osteoarthritis. Severity and distribution of joint damage was scored for each articular surface and related to potential prognostic factors, including varus deformity, the ligamentous status of the knee, age, gender and BMI. There was highly significant association between varus angulation of the knee and the total damage score for the tibia (P=0.001), but not the femur (P=0.2947). The degree of deformity, and not the status of the ACL alone, determines wear pattern and provides insight for preoperative planning of TKA.

Anteroposterior Knee Stability During Stair Descent.

This study examined the influence of tibio-femoral conformity on anteroposterior (AP) knee stability during stair descent, particularly with a dished cruciate sacrificing (CS) design. A joint simulator simulated stair descent of cadaveric knees. Tibio-femoral displacement was measured. Knees were tested in intact, ACL-deficient, and TKA with cruciate-retaining (CR), CS and posterior-stabilizing (PS) inserts. Loading during stair descent simulation caused femur displacement anteriorly prior to quadriceps contraction. Quadriceps contraction reestablished the initial femoral AP position. During simulated stair descent, AP stability was restored using PS, CR or CS inserts with an intact PCL. The CS design without the PCL did not provide AP stability. Increasing quadriceps force to restore AP stability may explain the clinical findings of pain and fatigue experienced by some patients after TKA.