A Sports Medicine Clinician's Guide to the Diagnosis and Management of Distal Clavicular Osteolysis.

ABSTRACT: Weightlifting associated shoulder injuries have seen a dramatic rise in the last 20 years. Distal clavicular osteolysis, coined weightlifter's shoulder, is one such condition caused by repetitive microtrauma to the distal clavicle with subsequent, painful development of bony erosions and resorption of the distal clavicle. Diagnosis, treatment, and prevention of this condition can be challenging. In this article, we highlight evidence-based clinical recommendations for the diagnosis and management of distal clavicular osteolysis, including specific considerations for atraumatic and posttraumatic etiologies, to help clinicians better care for their patients. Activity modification and rehabilitation are the mainstays of the initial treatment. Adjuvant treatments, such as injections or surgery, may be required in refractory cases or in certain patient populations. Early recognition and treatment of weightlifter's shoulder is essential to prevent progression to acromioclavicular joint pathology or instability and to allow for continued participation in sport-specific activities.

Bone lesions in hairy cell leukemia: Diagnosis and treatment.

Skeletal involvement is a rare complication of hairy cell leukemia (HCL) with an incidence of approximately 3%. Bone lesions are commonly lytic, and the most common sites of involvement are the femoral head and neck. Skeletal involvement is typically associated with high tumor burden and bone marrow infiltration. However, isolated cases of skeletal disease without splenomegaly or bone marrow involvement are occasionally reported. This review focuses on skeletal lesions in HCL, particularly the pathogenesis, clinical symptoms, diagnostic methods, and treatment approach. A literature review of the MEDLINE database for articles in English concerning hairy cell leukemia, skeletal symptoms, bone involvement was conducted via PubMed. Publications from January 1970 to May 2020 were scrutinized. Additional relevant publications were obtained by reviewing the references from the chosen articles.

Role of (Neo)adjuvant Denosumab for Giant Cell Tumor of Bone.

OPINION STATEMENT: Denosumab is a RANK ligand inhibitor approved for the treatment of giant cell tumor of bone. While the role of denosumab in the setting of advanced and unresectable disease is well established, its role in surgically resectable disease is currently under discussion. Several prospective and retrospective series on neoadjuvant therapy in potentially resectable tumor with high morbidity surgery reported a relapse rate of 10-20% after resection and 30-40% after curettage. At the same time, less morbid surgery has obvious clinical advantages for the patient, and several studies have shown the efficacy of denosumab in downgrading of the surgical procedure. Currently, the role of neoadjuvant denosumab in operable GCTB is limited to selected cases in which a diffuse reactive bone formation and peripheral ossification can make an easier surgical procedure, for example, in tumors with a large soft tissue component. A planned resection may become less morbid when preoperative denosumab is administered. Whenever a segmental resection is thought to be indicated at diagnosis, denosumab may be considered in the neoadjuvant setting. A preoperative course of 6 months is considered safe and effective. Two case scenarios are presented and critically discussed. Because of the high recurrence rates after denosumab treatment followed by curettage, we discourage the use of denosumab when curettage is considered feasible. In this setting, a short course of preoperative denosumab (2-6 months) may be considered for highly selected cases, for example in pathological fractures. The role of adjuvant denosumab needs further investigation. Long-term disease control has been reported in case of non-surgical lesions, even after treatment interruption, but there is no consensus on ideal treatment duration and dosage for these scenarios. In all cases, multidisciplinary discussion with oncology, pathologist, radiologist, and surgeons is mandatory. Patient's comorbidities, dental conditions, and preferences, including family planning, should always be taken into account.

A vitamin E blended highly cross-linked polyethylene acetabular cup results in less wear: 6-year results of a randomized controlled trial in 199 patients.

Background and purpose - Survivorship of total hip arthroplasty (THA) with the ultra-high molecular weight polyethylene (UHMWPE) monoblock cup has been limited due to periprosthetic osteolysis and aseptic loosening, secondary to wear of the UHMWPE. In response, a vitamin E blended highly cross-linked polyethylene (HXLPE) cup was developed. This study set out to compare the wear and clinical 6-year outcomes of vitamin E blended HXLPE with UHMWPE in an isoelastic monoblock cup in patients with hip osteoarthritis who underwent uncemented THA. The 2-year results have been reported previously. Patients and methods - For this randomized controlled trial 199 patients were included. 102 patients received the vitamin E blended HXLPE uncemented acetabular cup and 97 patients the uncemented UHMWPE monoblock cup. Clinical and radiographic parameters were obtained preoperatively, directly postoperatively, and at 3, 12, 24, and 72 months. Wear rates were compared using the femoral head penetration (FHP) rate. Results - 173 patients (87%) completed the 6-year follow-up. The mean NRS scores for rest pain, load pain, and patient satisfaction were 0.3 (SD 1), 0.6 (SD 1), and 8.6 (SD 1) respectively. The mean Harris Hip Score was 93 (SD 12). The FHP rate was lower in the vitamin E blended HXLPE cup (0.028 mm/year) compared with the UHMWPE cup (0.035 mm/year) (p = 0.002). No adverse reactions associated with the clinical application of vitamin E blended HXLPE were observed. 15 complications occurred, equally distributed between the two cups. The 6-year survival to revision rate was 98% for both cups. There was no aseptic loosening. Interpretation - This study shows the superior performance of the HXLPE blended with vitamin E acetabular cup with clinical and radiographic results similar to the UHMWPE acetabular cup.

Pubic osteolysis simulating a malignant lesion. A case report with long-term follow-up.

Pubic osteolysis is a rare pathology characterized by a painful radiographic destructive changes in the pubic rami, pubis or pubic symphysis that often follows a post-traumatic event. The etiology is unclear but it is a benign lesion, frequently misinterpreted as malignant. We report a case of a 54-year-old woman with pubic osteolysis mimicking a malignant lesion, diagnosed after open bone biopsy, conservatively treated without any sequelae and followed-up 10 years after the end of treatment. Although in the majority of the reported cases, a previous trauma has been commonly referred, in our case the patient did not refer to any cause before the onset of clinical symptoms. Knowledge of this entity is important to avoid invasive diagnostic procedures, costly investigations or overtreatment.

Case report: Fever- pneumonia- lymphadenectasis- osteolytic- subcutaneous nodule: Disseminated chromoblastomycosis caused by phialophora.

Chromoblastomycosis (CBM) is a chronic cutaneous and subcutaneous fungal infection caused by certain dematiaceous fungi (usually Fonsecaea, Phialophora, or Cladophialophora). Histologically, CBM is characterized by the presence of medlar bodies. However, the diagnosis is difficult because of the rarity of these pathognomonic presentations and the wide variety of presentations. Treatment of these infections is challenging as it lacks standardization. Herein, we report a case of chromoblastomycosis caused by Phialophora, in a 42-year-old immunocompetent male agriculturist from the humid and subtropical region of southern China. He had a 3-month history of pneumonia with intermittent fever, coughing, and expectoration. The infection subsequently spread to the bone and lymph nodes forming deep lesions and eventually resulting in osteolysis and lymphadenectasis. These subcutaneous nodules were observed after 9 months. Antifungal treatment was administered for 20 months leading to clinical improvement before the patient was lost to follow-up. This case is unique because such deep lesions are rare in immunocompetent individuals and because the initial onset was associated with pneumonia.

The 2018 Otto Aufranc Award: How Does Genome-wide Variation Affect Osteolysis Risk After THA?

BACKGROUND: Periprosthetic osteolysis resulting in aseptic loosening is a leading cause of THA revision. Individuals vary in their susceptibility to osteolysis and heritable factors may contribute to this variation. However, the overall contribution that such variation makes to osteolysis risk is unknown. QUESTIONS/PURPOSES: We conducted two genome-wide association studies to (1) identify genetic risk loci associated with susceptibility to osteolysis; and (2) identify genetic risk loci associated with time to prosthesis revision for osteolysis. METHODS: The Norway cohort comprised 2624 patients after THA recruited from the Norwegian Arthroplasty Registry, of whom 779 had undergone revision surgery for osteolysis. The UK cohort included 890 patients previously recruited from hospitals in the north of England, 317 who either had radiographic evidence of and/or had undergone revision surgery for osteolysis. All participants had received a fully cemented or hybrid THA using a small-diameter metal or ceramic-on-conventional polyethylene bearing. Osteolysis susceptibility case-control analyses and quantitative trait analyses for time to prosthesis revision (a proxy measure of the speed of osteolysis onset) in those patients with osteolysis were undertaken in each cohort separately after genome-wide genotyping. Finally, a meta-analysis of the two independent cohort association analysis results was undertaken. RESULTS: Genome-wide association analysis identified four independent suggestive genetic signals for osteolysis case-control status in the Norwegian cohort and 11 in the UK cohort (p ≤ 5 x 10). After meta-analysis, five independent genetic signals showed a suggestive association with osteolysis case-control status at p ≤ 5 x 10 with the strongest comprising 18 correlated variants on chromosome 7 (lead signal rs850092, p = 1.13 x 10). Genome-wide quantitative trait analysis in cases only showed a total of five and nine independent genetic signals for time to revision at p ≤ 5 x 10, respectively. After meta-analysis, 11 independent genetic signals showed suggestive evidence of an association with time to revision at p ≤ 5 x 10 with the largest association block comprising 174 correlated variants in chromosome 15 (lead signal rs10507055, p = 1.40 x 10). CONCLUSIONS: We explored the heritable biology of osteolysis at the whole genome level and identify several genetic loci that associate with susceptibility to osteolysis or with premature revision surgery. However, further studies are required to determine a causal association between the identified signals and osteolysis and their functional role in the disease. CLINICAL RELEVANCE: The identification of novel genetic risk loci for osteolysis enables new investigative avenues for clinical biomarker discovery and therapeutic intervention in this disease.

Tunnel osteolysis post-ACL reconstruction: a systematic review examining select diagnostic modalities, treatment options and rehabilitation protocols.

PURPOSE: The purpose of this systematic review was to (1) identify the optimal diagnostic modality for tunnel widening in skeletally mature patients; (2) identify potentially modifiable risk factors for tunnel widening, such as graft type, and (3) determine what elements of a post-operative rehabilitation program exert the most influence on TW. METHODS: The electronic databases MEDLINE, EMBASE, PubMed, and Cochrane Library were searched from database inception to January 2018. Studies that discussed tunnel widening following anterior cruciate ligament reconstruction (ACLR) of skeletally mature patients and written in English were included. Descriptive statistics, such as means, ranges, and measures of variance (e.g. standard deviations, 95% confidence intervals (CI)) are presented where applicable. RESULTS: 103 studies (6,383 patients) were included. Plain radiographs were the most commonly used diagnostic modality, but radiographs on average required 10 months longer than CT and 2 months longer on average than MRI to diagnose tunnel widening after ACLR. Although CT was the least commonly used modality, it was the shortest time to diagnose tunnel widening at 9.5 months after ACLR. Bone-patellar tendon-bone (BPTB) allograft had the largest average tunnel widening overall. BPTB autograft had the lowest average tunnel widening overall. Double-bundle hamstring graft configuration had a lower average tunnel widening than single-bundle configuration. Rehabilitation protocols after ACLR that used a full weight-bearing prescription in rehabilitation showed a greater average femoral tunnel widening than partial weight-bearing, and partial weight-bearing showed a greater average tibial tunnel widening than full weight-bearing. CONCLUSIONS: Based on this systematic review and the descriptive data evaluated, CT demonstrated a time of 9.5 months on average from ACLR to diagnosing tunnel osteolysis post-ACLR. With respect to graft types, double-bundle hamstring autografts reported lower average femoral and tibial TW than single-bundle hamstring autografts. BPTB autografts reported the lowest average TW and BPTB allograft the largest average TW of all the grafts. Furthermore, extension-locked bracing had the lowest TW of all the brace protocols. Lastly, several other surgical technical parameters influencing tunnel osteolysis remain to be determined. No definitive recommendations can be made at this time due to the high heterogeneity of data and the lack of comparative studies analysed in this systematic review. LEVEL OF EVIDENCE: IV.

Pleomorphic clinical spectrum of metallosis in total hip arthroplasty.

PURPOSE: To summarize the biological effects of metal debris from hip arthroplasties which characterize a polymorphic clinical spectrum of local and remote manifestation. METHODS: Retrospective study. Patient, implant, and surgical characteristics were collected, including implant survival, clinical manifestations, cause of arthroplasty revision or implant failure, and peri- and intra-operative complications. The primary endpoint was implant survivorship. Hip revision arthroplasty was decided considering clinical signs and symptoms, abnormal imaging (XR, MR, TC, echotomography, scintigraphy), and blood metal ion level. An ad hoc electronic form was used to collect demographic, epidemiological, and clinical variables. In-between group comparisons of quantitative variables were performed with the Student t test and the Mann-Whitney for parametric and non-parametric variables, respectively. Logistic regression analyses were carried out to assess the relationship between clinical and radiographic characteristics and stem and cup revision. Radiographic measurements of implant positioning validity and reliability were assessed using Krippendorff's alpha reliability coefficient. The statistical software STATA version 15 (StatsCorp, TX) was used to perform statistical computations. RESULTS: In this MoM THA series, the most incident cause of implant failure was ARMD in 11 out of 14 (78.6%) patients. All clinical failure manifestations, revision surgery highlights, and intra-operative findings are reported. CONCLUSIONS: The local adverse reactions include lesions of different clinical relevance from small asymptomatic soft tissue lesions to dramatic osteolysis, necrosis, effusion, and growing masses which can cause secondary pathological effects. Symptoms of systemic toxicity are rarely described but may have been largely unreported in literature. Despite the extensive literature on the topic, the patient's management is still uncertain and challenging. Every metallic implant (e.g., screws, plates, spinal instrumentations) has a potential local or systemic adverse effect. Organizing a national registry of arthroplasty should be mandatory, in order to collect data about the patients, the surgery, the implanted device (with a careful post-marketing tracking), and the follow-up for all the procedures performed at a national level. The data collected in the registry will allow to analyze the implant survival and to better recognize the undesirable and sometimes unexpected effects of different biomaterials on the whole body.

Trends in total hip arthroplasty.

This article discusses developments in total hip arthroplasty related to the use of highly cross-linked polyethylene (HXLPE) liner material as the new standard of care for acetabular cup articulation surfaces. The pathologic implications of metal-on-metal hip prostheses in asymptomatic patients also are discussed.

The C-Terminal Intact Forms of Periostin (iPTN) Are Surrogate Markers for Osteolytic Lesions in Experimental Breast Cancer Bone Metastasis.

Periostin is an extracellular matrix protein that actively contributes to tumor progression and metastasis. Here, we hypothesized that it could be a marker of bone metastasis formation. To address this question, we used two polyclonal antibodies directed against the whole molecule or its C-terminal domain to explore the expression of intact and truncated forms of periostin in the serum and tissues (lung, heart, bone) of wild-type and periostin-deficient mice. In normal bones, periostin was expressed in the periosteum and specific periostin proteolytic fragments were found in bones, but not in soft tissues. In animals bearing osteolytic lesions caused by 4T1 cells, C-terminal intact periostin (iPTN) expression disappeared at the invasive front of skeletal tumors where bone-resorbing osteoclasts were present. In vitro, we found that periostin was a substrate for osteoclast-derived cathepsin K, generating proteolytic fragments that were not recognized by anti-periostin antibodies directed against iPTN. In vivo, using an in-house sandwich immunoassay aimed at detecting iPTN only, we observed a noticeable reduction of serum periostin levels (- 26%; P < 0.002) in animals bearing osteolytic lesions caused by 4T1 cells. On the contrary, this decrease was not observed in women with breast cancer and bone metastases when periostin was measured with a human assay detecting total periostin. Collectively, these data showed that mouse periostin was degraded at the bone metastatic sites, potentially by cathepsin K, and that the specific measurement of iPTN in serum should assist in detecting bone metastasis formation in breast cancer.

Osteolytic Lesions in Primary Myelofibrosis and Effect of Ruxolitinib Therapy: Report of a Case and Literature Review.

Here, we report the case of a young female affected by primary myelofibrosis (PMF) who developed an osteolytic lesion of the humerus during the follow-up, and the possible efficacy of ruxolitinib in controlling this rare event. After 26 years of follow-up, the patient reported onset of acute pain at the proximal region of the left upper limb. An X-ray revealed an osteolytic bone lesion in the proximal third of the humeral shaft, which was then confirmed by magnetic resonance imaging. A biopsy of the lytic lesion was done, revealing hypercellular bone marrow with hyperplastic granulopoiesis associated with megakaryocytic proliferation and atypia, accompanied by a diffuse and dense increase in reticulin fibrosis with extensive intersections and coarse bundles of thick fibers, consistent with a grade 3 collagen fibrosis. No new therapeutic intervention was initially required; however, 2 years later, the patient reported symptomatic splenomegaly and drenching night sweats, so ruxolitinib therapy was started. By week 8, the patient had near resolution of constitutional symptoms and a reduction of > 50% of the spleen size that normalized by 6 months; in addition, a repeat bone marrow biopsy showed a decrease in reticulin fibrosis grade. Interestingly, after 9 months of ruxolitinib therapy, further magnetic resonance imaging of the left upper limb showed the absence of bone lytic lesions and a substantial normalization of the bone tissue. In conclusion, with the present case report, we confirm ruxolitinib efficacy in reducing bone marrow fibrosis grade and assume its possible role in the resolution of osteolytic lesions in PMF. Obviously, further studies with a greater number of patients are needed to document the exact frequency of these unusual findings and the possible role of ruxolitinib in their treatment.

Posterior dislocation following revision total knee replacement arthroplasty: a case report and literature analysis.

Knee dislocation following total knee replacement arthroplasty is a rare but serious complication. The incidence of dislocation following primary total knee arthroplasty with posterior stabilized implants ranges from 0.15 to 0.5%, and posterior dislocation after revision total knee arthroplasty is even rarer. Here, we report the case of a 76-year-old male who presented with posterior dislocation after posterior stabilized revision total knee arthroplasty.

Identical Presentation of Scapular Osteolysis in Two Patients with Thoracic Kaposiform Hemangioendothelioma.

Kaposiform hemangioendothelioma (KHE) is a rare, locally aggressive vascular tumor that does not metastasize. We report two unique cases of KHE involving the right hemithorax and the upper ipsilateral extremity. Kasabach-Merrit phenomenon and osteolytic lesions in the scapula were observed in both cases.

Osteolytic Sarcoidosis of the Orbital Roof Masquerading as a Malignant Orbital Lesion.

A 51-year-old man without a significant past medical history presented with 4 weeks of progressive swelling and drooping of his left upper eyelid. A CT of the left orbit revealed an osteolytic mass lesion in the area of the lacrimal gland. A left orbitotomy with excisional biopsy was performed. The excised tissue was sent for infectious workup and histopathological examination, which revealed osteolytic sarcoidosis. The patient was treated with systemic and local injection corticosteroids, and followed over 10 months without evidence of recurrence. Systemic workup with CT of his chest, abdomen, and pelvis revealed no further evidence of sarcoidosis. To the best of the authors knowledge, this is the first report of an otherwise healthy patient presenting with isolated osteolytic sarcoidosis of the orbit and a negative systemic workup.

Circulating sRAGE in the diagnosis of osteolytic bone metastasis.

Despite the clinical importance of metastasis to the skeleton, the diagnostic tools for early detection and monitoring of bone metastasis lack sensitivity and specificity. We evaluated a promising new serum biomarker, the soluble form of the Receptor of Advanced Glycosylated End-products (sRAGE). sRAGE is involved in the Wnt-signaling pathway, and has been reported to reduce the risk of cancer. We investigated the diagnostic potential of sRAGE to improve the detection and monitoring of bone metastasis. We measured sRAGE in the serum of control healthy subjects, patients with primary tumors and patients with bone metastasis. sRAGE was also correlated with the Wnt inhibitors DKK-1 and sclerostin, the bone resorption markers MMP-2, MMP-9 and TRAP5, and the metastatic marker survivin. sRAGE was significantly lower in primary tumor and metastatic patients than in healthy subjects. sRAGE also showed a strong negative correlation with DKK-1, sclerostin, MMP-2, MMP-9, TRAP5b and survivin. These results indicated that sRAGE might play a protective role in bone metastasis progression, and it may diagnostic significance for detecting and monitoring osteolytic metastases.

Do cobalt and chromium levels predict osteolysis in metal-on-metal total hip arthroplasty?

INTRODUCTION: Serum metal ions are part of the regular follow-up routine of patients with metal-on-metal total hip arthroplasties (MoM-THA). Increased cobalt levels have been suggested to indicate implant failure and corrosion. QUESTIONS: (1) Is there a correlation between the size of the osteolysis measured on a CT scan and metal ion levels? (2) Can metal ion levels predict the presence of osteolysis in MoM-THA? (3) Are cobalt and chromium serum levels or the cobalt-chromium-ratio diagnostic for osteolysis? MATERIALS AND METHODS: CT scans of patients (n = 75) with a unilateral MoM-THA (Birmingham Hip System, Smith & Nephew, TN, USA) implanted by a single surgeon were reviewed to determine the presence of osteolysis. Statistical analysis was performed to detect its association with metal ion levels at the time of the imaging exam. RESULTS: The incidence of osteolysis was the same in men and women (35.6 vs 35.7 %). The cobalt-chromium-ratio correlates with the size of the osteolysis on the CT scan and the femoral component size in the overall study population (p = 0.050, p = 0.001) and in men (p = 0.002, p = 0.001) but not in women (p = 0.312, p = 0.344). The AUC for the cobalt-chromium-ratio to detect osteolysis was 0.613 (p = 0.112) for the overall population, 0.710 for men (p = 0.021) and 0.453 (p = 0.684) for women. The data suggest that a cut off level of 1.71 for the cobalt-chromium-ratio has a sensitivity of 62.5 % and specificity of 72.4 % to identify male patients with osteolysis. CONCLUSIONS: The disproportional increase of cobalt over chromium, especially in male patients with large component sizes can not be explained by wear alone and suggests that other processes (corrosion) might contribute to metal ion levels and might be more pronounced in patients with larger component sizes.

[Patellar bone deficiency in revision total knee arthroplasty]. / Patellarekonstruktion bei defizientem knöchernen Lager.

BACKGROUND: Patellar bone deficiency in revision total knee arthroplasty (TKA) determines the surgical procedure. Different reconstructive and ablative techniques, dependent on the remaining bone stock, are described. INDICATION: The primary patella implant can be retained in up to 50 % of revision situations. Reasons for replacement are aseptic and septic loosening, implant failure, expanding osteolysis, maltracking of the patella and "metal-backed" prosthesis. The aim of the reconstruction is the stable fixation and proper tracking of the implant by restoring the extensor mechanism. SURGICAL PROCEDURE: Dependent on the extent of bone loss and the availability of a patellar rim, the following surgical procedures are recommended. When the remaining bone thickness is 10 mm or more: implantation of a polyethylene "onlay-type" patella; when it is between 6-9 mm and there is an intact patellar rim: reconstruction with a biconvex "inlay-type" patella implant, where the biconvex shape replaces the bone defect partially. When there is deficient bone stock (less than 6 mm) or no cortical patellar rim then augmenting procedures with autologous spongiosa and procedures such as "impaction bone grafting", "trabecular metal" prosthesis, where the trabecular part of the implant serves as the base for the cemented polyethylene button, "gull-wing" osteotomy, which is an adapting and configuring technique of osteotomy; and in exceptional cases patelloplasty or patellectomy are used. CONCLUSION: Regarding the importance of the patellar component in biomechanics of the joint and function of the extensor mechanism, the reconstruction of the patella should be the primary aim. Patelloplasty or patellectomy should be avoided.

Ballooning osteolysis in 71 failed total ankle arthroplasties.

Background and purpose - Aseptic loosening is a major cause of failure in total ankle arthroplasty (TAA). In contrast to other total joint replacements, large periarticular cysts (ballooning osteolysis) have frequently been observed in this context. We investigated periprosthetic tissue responses in failed TAA, and performed an element analysis of retrieved tissues in failed TAA. Patients and methods - The study cohort consisted of 71 patients undergoing revision surgery for failed TAA, all with hydroxyapatite-coated implants. In addition, 5 patients undergoing primary TAA served as a control group. Radiologically, patients were classified into those with ballooning osteolysis and those without, according to defined criteria. Histomorphometric, immunohistochemical, and elemental analysis of tissues was performed. Von Kossa staining and digital microscopy was performed on all tissue samples. Results - Patients without ballooning osteolysis showed a generally higher expression of lymphocytes, and CD3+, CD11c+, CD20+, and CD68+ cells in a perivascular distribution, compared to diffuse expression. The odds of having ballooning osteolysis was 300 times higher in patients with calcium content >0.5 mg/g in periprosthetic tissue than in patients with calcium content ≤0.5 mg/g (p < 0.001). Interpretation - There have been very few studies investigating the pathomechanisms of failed TAA and the cause-effect nature of ballooning osteolysis in this context. Our data suggest that the hydroxyapatite coating of the implant may be a contributory factor.