Taper design affects failure of large-head metal-on-metal total hip replacements.

BACKGROUND: Large-head metal-on-metal (MoM) hip arthroplasties have demonstrated poor survival. Damage at the taper-trunnion junction is a contributing factor; however, the influence of junction design is not well understood. QUESTIONS/PURPOSES: (1) Does taper type affect fretting, corrosion, and volumetric wear at the junction? (2) Do taper types have different wear patterns? (3) Does larger offset or head diameter increase fretting, corrosion, and wear? (4) Is the extent of fretting and corrosion associated with earlier failure? METHODS: Taper damage in 40 retrieved heads was subjectively graded for fretting and corrosion, and wear was determined with high-resolution confocal measurement. Taper types (11/13, 12/14, and Type 1) differed by angle, distal diameter, and contact length; Type 1 were thinnest and 11/13 had longer contact lengths. RESULTS: Fretting scores were higher in 11/13 than in Type 1 tapers. Volumetric wear and wear rates did not differ among types. Uniform, circumferential, and longitudinal wear patterns were observed in all types, but fretting, corrosion, and wear did not differ among the patterns. Head diameter and lateral offset did not correlate with fretting, corrosion, or wear. No correlation was found between fretting, corrosion, or wear and length of implantation. CONCLUSIONS: In general, thicker tapers with longer contact lengths were associated with greater fretting scores, whereas no relationship was found among the three designs for corrosion scores or volumetric wear. This finding suggests that trunnion diameter and engagement length are important factors to consider when improving taper-trunnion junction design.

What causes unexplained pain in patients with metal-on metal hip devices? A retrieval, histologic, and imaging analysis.

BACKGROUND: Adverse tissue reactions associated with metal-on-metal (MOM) hips are common in resurfacing and total hip arthroplasty (THA) designs. The etiology of these reactions in painful, well-positioned arthroplasties is inconsistently described. QUESTIONS/PURPOSES: The purposes of this study were to compare the (1) articular wear rates; (2) histologic findings; (3) synovial response on MRI; and (4) graded intraoperative tissue damage between well-positioned, MOM hips revised for unexplained pain and MOM hips revised for other reasons and to (5) determine whether the presence of a taper junction on a MOM articulation affects these four parameters in unexplained pain. METHODS: We retrospectively studied 88 patients (94 hips) who had undergone revision of either a hip resurfacing or a large-head (> 36 mm) THA. Thirty-five hips revised for unexplained pain were compared with a control group of 59 hips revised for other causes. Articular wear was measured using three-dimensional contactless metrology and histologic analysis was performed using the aseptic lymphocyte-dominated vasculitis-associated lesion (ALVAL) score. Preoperative MRI was performed on 57 patients to determine synovial volumes and thicknesses. Tissue damage was graded from intraoperative reports. RESULTS: Articular wear rates in the unexplained pain group were lower than in the control group (median 2.6 µm/year versus 12.8 µm/year, p < 0.001). Sixty-six percent of patients in the unexplained pain group had histologic confirmation of ALVAL compared with 19% in the control group (p < 0.001). The synovial thickness on MRI was higher in the unexplained pain group (p = 0.04) and was highly predictive of ALVAL. Severe intraoperative tissue damage was noted in more cases in the unexplained pain group (p = 0.01). There were no differences in articular wear, histology, MRI, and tissue damage between resurfacings and THAs revised for unexplained pain. CONCLUSIONS: Unexplained pain in patients with well-positioned MOM hips warrants further investigation with MRI to look for features predictive of ALVAL. Tissue destruction in these cases does not appear to be related to high bearing wear or the presence of a taper.

Rotating-platform has no surface damage advantage over fixed-bearing TKA.

BACKGROUND: Rotating-platform TKA, although purported to have superior kinematics, has shown no clinical advantages over those of fixed-bearing TKA. Our design-matched retrieval study aimed to investigate if differences in bearing wear damage exist between fixed- and mobile-bearing TKAs with similar condylar geometry. QUESTIONS/PURPOSES: We asked whether (1) the rotating platform's more conforming tibiofemoral articulation would be associated with less severe damage; (2) the location of damage and wear would be similar on the tibiofemoral or backside surfaces of two contemporary designs with similar condylar geometry; and (3) the combined damage and deformation measured as thickness would differ between the two designs. METHODS: We performed damage grading and damage mapping on 25 rotating-platform and 17 fixed-bearing inserts. The patient demographic data from each of these cohorts were comparable. Inserts were also laser-scanned from which we obtained thicknesses, and inferior surface three-dimensional scans, from which we determined dimensional changes. RESULTS: Rotating-platform and fixed-bearing inserts had similar tibiofemoral damage scores. However, the scores on the inferior surface of rotating platforms were greater, often as a result of third-body debris scratching observed on both damage mapping and three-dimensional scans. The extent of damage as a function of surface area was greater for rotating platforms, consistent with the greater tibiofemoral conformity. Dimensional changes on the inferior surfaces of the fixed bearing followed loading areas of the knee. However, no differences were seen in the thicknesses between fixed- and rotating-platform bearings. CONCLUSIONS: The increased total damage score on the rotating platform, coupled with increased surface area damaged and the propensity for third-body debris, indicates no damage advantage to this mobile-bearing design.

Laser scanning as a useful tool in implant retrieval analysis: a demonstration using rotating platform and fixed bearing tibial inserts.

Objective methods for analyzing arthroplasty retrieval implants are needed. To address this, we used a readily available laser scanner to analyze damage deviations between cohorts of rotating platform and fixed bearing inserts previously analyzed using traditional, subjective retrieval analysis methods. We asked the following research questions: 1) Do articular surface deviations measured by the scanner correlate with the subjective damage scores? 2) Do articular surface deviations differ between inserts due to design differences? Correlations between deviations and damage scores were present in RP but not FB inserts. Seven different deviation patterns were present between the RP and FB inserts and were a function of design. In conclusion laser scanning was found to be a useful objective tool for analyzing arthroplasty retrievals.

A comprehensive finite element model of surgical treatment for cervical myelopathy.

BACKGROUND: Cervical myelopathy is a common and debilitating chronic spinal cord dysfunction. Treatment includes anterior and/or posterior surgical intervention to decompress the spinal cord and stabilize the spine, but no consensus has been made as to the preferable surgical intervention. The objective of this study was to develop an finite element model of the healthy and myelopathic C2-T1 cervical spine and common anterior and posterior decompression techniques to determine how spinal cord stress and strain is altered in healthy and diseased states. METHODS: A finite element model of the C2-T1 cervical spine, spinal cord, pia, dura, cerebral spinal fluid, and neural ligaments was developed and validated against in vivo human displacement data. To model cervical myelopathy, disc herniation and osteophytes were created at the C4-C6 levels. Three common surgical interventions were then incorporated at these levels. FINDINGS: The finite element model accurately predicted healthy and myelopathic spinal cord displacement compared to motions observed in vivo. Spinal cord strain increased during extension in the cervical myelopathy finite element model. All surgical techniques affected spinal cord stress and strain. Specifically, adjacent levels had increased stress and strain, especially in the anterior cervical discectomy and fusion case. INTERPRETATIONS: This model is the first biomechanically validated, finite element model of the healthy and myelopathic C2-T1 cervical spine and spinal cord which predicts spinal cord displacement, stress, and strain during physiologic motion. Our findings show surgical intervention can cause increased strain in the adjacent levels of the spinal cord which is particularly worse following anterior cervical discectomy and fusion.

Implantation Time Has No Effect on the Morphology and Extent of Previously Reported "Degradation" of Prolene Pelvic Mesh.

OBJECTIVES: Prolene polypropylene ("Prolene") meshes demonstrate no in vivo degradation, yet some claim degradation continues until no more Prolene polypropylene can be oxidized. We studied whether implantation time affects the morphology/extent of previously reported as cracking/degradation of completely cleaned Prolene explants. METHODS: Urogynecological explants (248 patients) were collected. After excluding non-Prolene/unknown meshes and those without known implantation times, completely cleaned explants (n = 205; 0.2-14.4 years implantation) were analyzed with light microscopy, scanning electron microscopy, and Fourier transform infrared spectroscopy. Based on implant times and storage (fixative or dry), representative specimens were randomly selected for comparison. Controls were unused ("exemplar") TVT specimens with and without intentional oxidation via ultraviolet light exposure. RESULTS: Prolene explants included 31 dry (18 TVT; 7 Prolift; 4 Gynemesh; 2 others) and 174 wet (87 TVT; 47 Prolift; 10 Gynemesh; 30 others) specimens. Specimens had similar morphologies before cleaning. Progressive cleaning removed tissue and cracked tissue-related material exposing smooth, unoxidized, and nondegraded fibers, with no visible gradient-type/ductile damage. Fourier transform infrared spectroscopy of the explants confirmed progressive loss of proteins. Cleaning intentionally oxidized exemplars did not remove oxidized carbonyl frequencies and showed deep cracks and gross fiber rupture/embrittlement, unlike the explants and nonoxidized exemplars. CONCLUSIONS: If in vivo Prolene degradation exists, there should be wide-ranging crack morphology and nonuniform crack penetration, as well as more cracking, degradation, and physical breakage for implants of longer implantation times, but this was not the case. There is no morphologic or spectral/chemical evidence of Prolene mesh degradation after up to 14.4 years in vivo.

Measurement of in vivo spinal cord displacement and strain fields of healthy and myelopathic cervical spinal cord.

OBJECTIVE: Cervical myelopathy (CM) is a common and debilitating form of spinal cord injury caused by chronic compression; however, little is known about the in vivo mechanics of the healthy spinal cord during motion and how these mechanics are altered in CM. The authors sought to measure 3D in vivo spinal cord displacement and strain fields from MR images obtained during physiological motion of healthy individuals and cervical myelopathic patients. METHODS: Nineteen study participants, 9 healthy controls and 10 CM patients, were enrolled in the study. All study participants had 3T MR images acquired of the cervical spine in neutral, flexed, and extended positions. Displacement and strain fields and corresponding principal strain were obtained from the MR images using image registration. RESULTS: The healthy spinal cord displaces superiorly in flexion and inferiorly in extension. Principal strain is evenly distributed along the spinal cord. The CM spinal cord displaces less than the healthy cord and the magnitude of principal strain is higher, at the midcervical levels. CONCLUSIONS: Increased spinal cord compression during cervical myelopathy limits motion of the spinal cord and increases spinal cord strain during physiological motion. Future studies are needed to investigate how treatment, such as surgical intervention, affects spinal cord mechanics.

Baseline and postfusion opioid burden for patients with low back pain.

OBJECTIVES: To evaluate opioid usage patterns for patients with low back pain (LBP) with and without spinal fusion surgery (fusion patients and nonfusion patients, respectively), including long-term prescriptions post fusion. STUDY DESIGN: Claims data of outpatient pharmaceutical prescriptions from privately insured patients. METHODS: The 3-year utilization, cost, and morphine milligram equivalents (MME) of opioid prescriptions were evaluated for patients with LBP with and without lumbar fusion. For fusion patients, opioid prescriptions before and after fusion, as well as prescription use 3, 6, and 12 months following fusion surgery, were analyzed. RESULTS: Thirty-one percent of patients with LBP had opioid prescriptions within the first 6 months of initial diagnosis, which increased to 42.1% within 3 years. More than twice as many fusion patients as nonfusion patients filled opioid prescriptions (87.2% vs 41.5%; P <.001). Fusion patients had 62% and 48% more days with opioid dosages of at least 50 and at least 90 MME/day, respectively, than nonfusion patients (≥50 MME/day, 84 days vs 52 days; ≥90 MME/day, 50 days vs 34 days; both P <.001). Opioid burden was greater for fusion patients following surgery. Fusion patients continued to have 2 months' supply with at least 50 MME/day and 1 month's supply with at least 90 MME/day at least 12 months following surgery. CONCLUSIONS: The opioid burden in the LBP population is high and is further elevated in those who subsequently undergo fusion surgery. Long-term opioid prescriptions persisted in 27% of fusion patients 12 months post surgery. Efforts to identify efficacious alternative therapies to treat LBP may reduce the societal burden of chronic opioid use.

Volume of Brain Herniation After Decompressive Craniectomy in Patients with Traumatic Brain Injury.

BACKGROUND: The decompressive hemicraniectomy operation is highly effective in relieving refractory intracranial hypertension. However, one limitation of this treatment strategy is the requirement to perform a subsequent cranioplasty operation to reconstruct the skull defect-an expensive procedure with high complication rates. An implant that is capable of accommodated post-hemicraniectomy brain swelling, but also provides acceptable skull defect coverage after brain swelling abates, would theoretically eliminate the need for the cranioplasty operation. In an earlier report, the concept of using a thin, moveable plate implant for this purpose was introduced. METHODS: Measurements were obtained in a series of stroke patients to determine whether a plate offset from the skull by 5 mm would accommodate the observed post-hemicraniectomy brain swelling. The volume of brain swelling measured in all patients in the stroke series would be accommodated by a 5-mm offset plate. In the current report, we expanded our analysis to study brain swelling patterns in a different population of patients requiring a hemicraniectomy operation: those with traumatic brain injuries (TBI). RESULTS: We identified 56 patients with TBI and measured their postoperative brain herniation volumes. A moveable plate offset by 5 mm would create sufficient additional volume to accommodate the brain swelling measured in all but one patient. That patient had malignant intraoperative brain swelling and died the following day. CONCLUSIONS: These data suggest that a 5 mm offset plate will provide sufficient volume for brain expansion for almost all hemicraniectomy operations.

Volume of Brain Herniation in Patients with Ischemic Stroke After Decompressive Craniectomy.

BACKGROUND: Decompressive craniectomy procedures are performed in patients with malignant intracranial hypertension. A bone flap is removed to relieve pressure. Later, a second operation is performed to reconstruct the skull after brain swelling has resolved. This surgical treatment would be improved if it were possible to perform a single operation that decompressed the brain acutely and eliminated the need for a second operation. To design a device and procedure that achieve this objective, it is essential to understand how the brain swells after a craniectomy procedure. METHODS: We identified 20 patients with ischemic stroke who underwent a decompressive hemicraniectomy operation. Skull defect morphology and postoperative brain swelling were measured using computed tomography scan data. Additional intracranial volume created by placing a hypothetical cranial plate implant offset from the skull surface by 5 mm was measured for each patient. RESULTS: The average craniectomy area and brain herniation volume was 9999 ± 1283 mm2 and 30.48 ± 23.56 mL, respectively. In all patients, the additional volume created by this hypothetical implant exceeded the volume of brain herniation observed. CONCLUSIONS: These findings show that a cranial plate with a 5-mm offset accommodates the brain swelling that occurs in this patient population.

Effect of Surgery on Gait and Sensory Motor Performance in Patients With Cervical Spondylotic Myelopathy.

BACKGROUND: Cervical spondylotic myelopathy (CSM) is a common disease of aging that leads to gait instability resulting from loss of leg sensory and motor functions. The results of surgical intervention have been studied using a variety of methods, but no test has been reported that objectively measures integrative leg motor sensory functions in CSM patients. OBJECTIVE: To determine the feasibility of using a novel single leg squat (SLS) test to measure integrative motor sensory functions in patients with CSM before and after surgery. METHODS: Fifteen patients with CSM were enrolled in this prospective study. Clinical data and scores from standard outcomes questionnaires were obtained before and after surgery. Patients also participated in experimental test protocols consisting of standard kinematic gait testing, the Purdue pegboard test, and the novel SLS test. RESULTS: The SLS test protocol was well tolerated by CSM patients and generated objective performance data over short test periods. In patients who participated in postoperative testing, the group measures of mean SLS errors decreased following surgery. Gait velocity measures followed a similar pattern of group improvement postoperatively. Practical barriers to implementing this extensive battery of tests resulted in subject attrition over time. Compared with kinematic gait testing, the SLS protocol required less space and could be effectively implemented more efficiently. CONCLUSIONS: The SLS test provides a practical means of obtaining objective measures of leg motor sensory functions in patients with CSM. Additional testing with a larger cohort of patients is required to use SLS data to rigorously examine group treatment effects. ABBREVIATIONS: BW, body weightCSM, cervical spondylotic myelopathymJOA, modified Japanese Orthopedic AssociationSLS, single leg squat.

Effects of brain derived neurotrophic factor Val66Met polymorphism in patients with cervical spondylotic myelopathy.

Cervical spondylotic myelopathy (CSM) is the leading cause of spinal cord related disability in the elderly. It results from degenerative narrowing of the spinal canal, which causes spinal cord compression. This leads to gait instability, loss of dexterity, weakness, numbness and urinary dysfunction. There has been indirect data that implicates a genetic component to CSM. Such a finding may contribute to the variety in presentation and outcome in this patient population. The Val66Met polymorphism, a mutation in the brain derived neurotrophic factor (BDNF) gene, has been implicated in a number of brain and psychological conditions, and here we investigate its role in CSM. Ten subjects diagnosed with CSM were enrolled in this prospective study. Baseline clinical evaluation using the modified Japanese Orthopaedic Association (mJOA) scale, Nurick and 36-Item Short Form Health Survey (SF-36) were collected. Each subject underwent objective testing with gait kinematics, as well as hand functioning using the Purdue Peg Board. Blood samples were analyzed for the BDNF Val66Met mutation. The prevalence of the Val66Met mutation in this study was 60% amongst CSM patients compared to 32% in the general population. Individuals with abnormal Met allele had worse baseline mJOA and Nurick scores. Moreover, baseline gait kinematics and hand functioning testing were worse compared to their wild type counterpart. BDNF Val66Met mutation has a higher prevalence in CSM compared to the general population. Those with BDNF mutation have a worse clinical presentation compared to the wild type counterpart. These findings suggest implication of the BDNF mutation in the development and severity of CSM.

Intermittent PTH administration and mechanical loading are anabolic for periprosthetic cancellous bone.

The purpose of this study was to determine the individual and combined effects on periprosthetic cancellous bone of intermittent parathyroid hormone administration (iPTH) and mechanical loading at the cellular, molecular, and tissue levels. Porous titanium implants were inserted bilaterally on the cancellous bone of adult rabbits beneath a loading device attached to the distal lateral femur. The left femur received a sham loading device. The right femur was loaded daily, and half of the rabbits received daily PTH. Periprosthetic bone was evaluated up to 28 days for gene expression, histology, and µCT analysis. Loading and iPTH increased bone mass by a combination of two mechanisms: (1) Altering cell populations in a pro-osteoblastic/anti-adipocytic direction, and (2) controlling bone turnover by modulating the RANKL-OPG ratio. At the tissue level, BV/TV increased with both loading (+53%, p < 0.05) and iPTH (+54%, p < 0.05). Combined treatment showed only small additional effects at the cellular and molecular levels that corresponded to a small additive effect on bone volume (+13% compared to iPTH alone, p > 0.05). This study suggests that iPTH and loading are potential therapies for enhancing periprosthetic bone formation. The elucidation of the cellular and molecular response may help further enhance the combined therapy and related targeted treatment strategies.

Bone Plug Versus Suture-Only Fixation of Meniscal Grafts: Effect on Joint Contact Mechanics During Simulated Gait.

BACKGROUND: Meniscus allograft transplantation (MAT) is primarily undertaken to relieve the symptoms associated with meniscal deficiencies. However, its ability to restore normal knee joint contact mechanics under physiological loads is still unclear. PURPOSE: To quantify the dynamic contact mechanics associated with 2 commonly used fixation techniques in MAT of the medial compartment: transosseous suture fixation via bone plugs and suture-only fixation at the horns. STUDY DESIGN: Controlled laboratory study. METHODS: Physiological loads to mimic gait were applied across 7 human cadaveric knees on a simulator. A sensor placed on the medial tibial plateau recorded dynamic contact stresses under the following conditions: (1) intact meniscus, (2) MAT using transosseous suture fixation via bone plugs at the anterior and posterior horns, (3) MAT using suture-only fixation, and (4) total medial meniscectomy. A "remove-replace" procedure was performed to place the same autograft for both MAT conditions to minimize the variability in graft size, geometry, and material property and to isolate the effects of the fixation technique. Contact stress, contact area, and weighted center of contact stress (WCoCS) were quantified on the medial plateau throughout the stance phase. RESULTS: Knee joint contact mechanics were sensitive to the meniscal condition primarily during the first half of the gait cycle. After meniscectomy, the mean peak contact stress increased from 4.2 ± 1.2 MPa to 6.2 ± 1.0 MPa (P = .04), and the mean contact area decreased from 546 ± 132 mm2 to 192 ± 122 mm2 (P = .01) compared with the intact meniscus during early stance (14% of the gait cycle). After MAT, the mean contact stress significantly decreased with bone plug fixation (5.0 ± 0.7 MPa) but not with suture-only fixation (5.9 ± 0.7 MPa). Both fixation techniques partially restored the contact area, but bone plug fixation restored it closer to the intact condition. The location of WCoCS in the central cartilage region (not covered by the meniscus) shifted peripherally throughout the stance phase. Bone plug fixation exhibited correction to this peripheral offset, but suture-only fixation did not. CONCLUSION: Under dynamic loading, transosseous fixation at the meniscal horns provides superior load distribution at the involved knee compartment after meniscal transplantation compared with suture-only fixation. Particular attention should be directed to the ability of medial MAT to function during the early stance phase. CLINICAL RELEVANCE: Transosseous fixation via bone plugs provides superior load distribution of a transplanted meniscal allograft compared with suture fixation alone at time zero.