Factors associated with heterotopic bone formation following total hip replacement

Artificial intelligence in predicting postoperative heterotopic ossification following anterior cervical disc replacement

OBJECTIVE

This study aimed to develop and validate a machine learning (ML) model to predict high-grade heterotopic ossification (HO) following Anterior cervical disc replacement (ACDR).

METHODS

Retrospective review of prospectively collected data of patients undergoing ACDR or hybrid surgery (HS) at a quaternary referral medical center was performed. Patients diagnosed as C3-7 single- or multi-level cervical disc degeneration disease with > 2 years of follow-up and complete pre- and postoperative radiological imaging were included. An ML-based algorithm was developed to predict high grade HO based on perioperative demographic, clinical, and radiographic parameters. Furthermore, model performance was evaluated according to discrimination and overall performance.

RESULTS

In total, 339 ACDR segments were included (61.65% female, mean age 45.65 ± 8.03 years). Over 45.65 ± 8.03 months of follow-up, 48 (14.16%) segments developed high grade HO. The model demonstrated good discrimination and overall performance according to precision (High grade HO: 0.71 ± 0.01, none-low grade HO: 0.85 ± 0.02), recall (High grade HO: 0.68 ± 0.03, none-low grade HO: 0.87 ± 0.01), F1-score (High grade HO: 0.69 ± 0.02, none-low grade HO: 0.86 ± 0.01), and AUC (0.78 ± 0.08), with lower prosthesis‑endplate depth ratio, higher height change, male, and lower postoperative-shell ROM identified as the most important predictive features.

CONCLUSION

Through an ML approach, the model identified risk factors and predicted development of high grade HO following ACDR with good discrimination and overall performance. By addressing the shortcomings of traditional statistics and adopting a new logical approach, ML techniques can support discovery, clinical decision-making, and intraoperative techniques better.

Heterotopic Ossification After Cervical Total Disc Replacement at 7 Years-Prevalence, Progression, Clinical Implications, and Risk Factors

Background

Heterotopic ossification (HO) is a known risk following cervical total disc replacement (CTDR) surgery, but the cause and effect of HO are not well understood. Reported HO rates vary, and few studies are specifically designed to report HO. The effects on outcomes, and the risk factors for the development of HO have been hypothesized and reported in small-population, retrospective analyses, using univariate statistics.

Methods

Posthoc, multiple-phase analysis of radiographic, clinical, and demographic data for CTDR as it relates to HO was performed. HO was radiographically graded for 164 one-level and 225 two-level CTDR patients using the McAfee and Mehren system. Analysis was performed to correlate HO grades to clinical outcomes and to evaluate potential risk factors for the development of HO using demographics and baseline clinical measures.

Results

At 7 years, 1-level clinically relevant HO grades were 17.6% grade 3 and 11.1% grade 4. Two-level clinically relevant HO grades, evaluated using the highest patient grade, were 26.6% grade 3 and 10.8% grade 4. Interaction between HO and time revealed significance for neck disability index (NDI; P = .04) and Visual Analog Scale (VAS) neck pain (P = .02). When analyzed at each time point NDI was significant at 48-84 months and VAS neck at 60 months. For predictors 2 analyses were run; odds ratios indicated follow-up visit, male sex, and preoperative VAS neck pain are related to HO development, whereas hazard ratios indicated male sex, obesity, endplate coverage, levels treated, and preoperative VAS neck pain.

Conclusions

This is the largest study to report HO rates, and related outcomes and risk factors. To develop an accurate predictive model, further large-scale analyses need to be performed. Based on the results reported here, clinically relevant HO should be more accurately described as motion-restricting HO until a definitive link to outcomes has been established.

Incidence and risk factors for heterotopic ossification after total hip arthroplasty: a meta-analysis

BACKGROUND

This study aims to quantitatively summarize risk factors associated with heterotopic ossification after total hip arthroplasty.

METHODS

The computerized and additional manual searches were performed in Medline, Embase, CNKI, and Cochrane central database (all through March 2014) for potential studies. Studies eligible had to meet the quality assessment criteria by Newcastle-Ottawa Scale and to evaluate the risk factors for heterotopic ossification after total hip arthroplasty. Two reviewers independently extracted the relevant data and any disagreement was solved by consensus. Stata11.0 was used to perform all the statistical analyses.

RESULTS

Fourteen studies involving 6468 cases with total hip arthroplasty and 1939 heterotopic ossification (HOs) (30.0 %) were eligible and included in this meta-analysis. Our meta-analysis identified the significant increased risk factors for HO were male gender [odds ratio (OR) 2.11; 95 % confidence interval (CI) 1.80-2.48)], cemented implant (OR 1.48; 95 % CI 1.00-2.17), bilateral operations (OR 1.74; 95 % CI 1.24-2.45), ankylosing spondylitis (OR 1.90; 95 % CI 1.07-3.37) and ankylosed hip (OR 9.85; 95 % CI 2.61-37.24). Rheumatoid arthritis was protective for the development of HO (OR 0.51; 95 % CI 0.33-0.80). The other variables including age, use of NSAIDs, femoral neck fracture, previous hip fracture, hypertrophic osteoarthritis and osteophytes were identified not as the risk factors for development of HO (P > 0.05).

CONCLUSION

Patients involved with the above-mentioned medical conditions should be carefully paid close attention by surgeons to reduce HO after total hip arthroplasty.

LEVEL OF EVIDENCE

Level II, meta-analysis.

Radiation therapy for recurrent heterotopic ossification prophylaxis after partial metatarsal amputation

The formation of heterotopic ossification is a relatively common, yet rarely discussed, cause of re-ulceration after previous partial metatarsal amputation. Excessive bone growth at the amputation site has the potential to create an unwanted prominence on the weightbearing surface of the foot, intuitively increasing plantar pressure and placing the neuropathic patient at greater risk of re-ulceration and limb loss. The aim of the present study was to assess the efficacy of single-dose radiation therapy in preventing recurrent heterotopic ossification. The inclusion criteria consisted of a history of clinically relevant heterotopic ossification formation after partial metatarsal amputation with subsequent partial metatarsal amputation for heterotopic ossification resection, followed by prophylactic single-dose radiation therapy. Eleven consecutive patients meeting the inclusion criteria were identified for the present study. Before the intervention, 10 (91%) patients demonstrated formation of mid- to high-grade heterotopic ossification, and 9 (82%) patients exhibited an associated neuropathic ulceration. On follow-up at least 6 weeks after intervention, 2 (18%) patients exhibited low-grade heterotopic ossification reformation that was not clinically relevant and 9 (82%) did not show signs of heterotopic recurrence. Single-dose radiation therapy can help prevent the formation of heterotopic ossification in high-risk patients, acting as an effective adjunct to surgery in minimizing the risk of re-ulceration and re-amputation in the neuropathic patient.

Effect of a selective COX-2 inhibitor, celecoxib, on heterotopic ossification after total hip arthroplasty: a case-controlled study

Heterotopic ossification (HO) is a well-known complication of total hip arthroplasty (THA), especially when the direct lateral approach is used. In this study, we examined the effect of the selective COX-2 inhibitor, celecoxib, on the rates of HO after THA. A control group consisting of 108 patients that did not receive celecoxib was compared with a study group consisting of 106 patients that did receive celecoxib. We assessed the presence and grade of HO using the Brooker classification and Harris hip scores were determined pre- and postoperatively to better quantify clinical outcomes. In this retrospective study of prospectively collected data, celecoxib is associated with a significant reduction in the incidence of HO in patients undergoing THA.

The predictive power of preoperative hip range of motion for the development of heterotopic ossification

Postoperative development of heterotopic ossification can compromise the success of total hip arthroplasty (THA). Heterotopic ossification has been associated with decreased postoperative hip range of motion (ROM), potentially leading to poor patient satisfaction with outcome. Many risk factors predisposing to heterotopic ossification have been discussed in the literature, including sex, age, operative time, surgical approach, and preoperative function. The goal of this study was to examine if preoperative ROM is a risk factor for the development of severe heterotopic ossification after THA, and the impact of severe heterotopic ossification formation on the gain in ROM following THA. In a retrospective study of a single surgeon's 20-year experience, all patients who developed type III heterotopic ossification after THA were evaluated for hip ROM preoperatively and at 1-year follow-up. Total ROM was classified according to the modified Merle d'Aubigne score, and Harris Hip Scores were calculated. A statistically significant difference was found in preoperative external rotation in the study group compared to the control group (P<.001). At 1 year postoperatively, hip ROM differences were significant in external rotation (P<.001), internal rotation (P<.001), and abduction (P<.05). The modified Merle d'Aubigne score was significantly different between the groups (P<.001). Although many factors have been shown to influence the development of heterotopic ossification following THA, we found that a decrease in preoperative external rotation may point to an increased risk. Surgeons should consider this data when considering the use of prophylactic treatment to avoid the development of heterotopic ossification.

Complications of Bryan cervical disc replacement

The primary goals of cervical disc replacement are to avoid fusion in the affected segment, maintain the mobility and function of the involved cervical segments, allow patients to quickly return to routine activities and reduce or eliminate adjacent-segment disease. A large number of patients have already undergone, and more and more patients will in the future undergo, cervical disc replacement. The cervical device which best preserves movement, and has therefore been the device of choice, has been the Bryan cervical disc. Although a safe surgical technique has been demonstrated and favorable results of using the Bryan disc reported, some complications have also accompanied this arthroplasty. Complications of Bryan cervical disc replacement include those related to the operative approach and decompression process, loosening and failure of the device, postoperative kyphosis, heterotopic ossification, and loss of movement due to spontaneous fusion. In order to avoid these complications, strict patient selection criteria and a meticulous knowledge of anatomy are necessary.

Clinical significance of heterotopic ossification in cervical disc replacement: a prospective multicenter clinical trial

OBJECTIVE

Heterotopic ossification (HO) is a well-known complication in joint replacements, but its occurrence and clinical effect on cervical artificial discs has not yet been studied. The purpose of this study was to investigate the incidence of HO in cervical disc replacement, to identify any associated risk factors for HO, and to examine the relationship of HO with clinical outcomes.

METHODS

The patient data for this observational study were obtained from the original Bryan Disc Study by the European Consortium. Occurrence of HO was defined by the McAfee classification on the cervical lateral x-rays at 12 months after surgery. Secondary outcome measurements included Odom's criteria and the Medical Outcomes Study Short-Form 36-Item Health Survey.

RESULTS

Sixteen (17.8%) of the 90 studied patients experienced HO, and 6 (6.7%) of these patients experienced Grade 3 and 4 HO. Ten patients' (11%) artificial discs were shown to have movement of less than 2 degrees on flexion and extension cervical x-ray at 12 months, with 4 of these patients having HO of Grade 3 or 4. Male sex (chi2 = 4.1; P = 0.0407) and older patients (P = 0.023; odds ratio = 1.10; 95% confidence interval = 1.01-1.19) were associated with development of HO.

CONCLUSION

There is a strong association of the occurrence of HO with subsequent loss of movement of the implanted cervical artificial disc. We have found that sex and age are two possible risk factors in the development of HO after cervical disc replacement.

Clinical Significance of Heterotopic Ossification in Cervical Disc Replacement: A Prospective Multicenter Clinical Trial

OBJECTIVE:

Heterotopic ossification (HO) is a well-known complication in joint replacements, but its occurrence and clinical effect on cervical artificial discs has not yet been studied. The purpose of this study was to investigate the incidence of HO in cervical disc replacement, to identify any associated risk factors for HO, and to examine the relationship of HO with clinical outcomes.

METHODS:

The patient data for this observational study were obtained from the original Bryan Disc Study by the European Consortium. Occurrence of HO was defined by the McAfee classification on the cervical lateral x-rays at 12 months after surgery. Secondary outcome measurements included Odom's criteria and the Medical Outcomes Study Short-Form 36-Item Health Survey.

RESULTS:

Sixteen (17.8%) of the 90 studied patients experienced HO, and 6 (6.7%) of these patients experienced Grade 3 and 4 HO. Ten patients' (11%) artificial discs were shown to have movement of less than 2 degrees on flexion and extension cervical x-ray at 12 months, with 4 of these patients having HO of Grade 3 or 4. Male sex (χ2 = 4.1; P = 0.0407) and older patients (P = 0.023; odds ratio = 1.10; 95% confidence interval = 1.01–1.19) were associated with development of HO.

CONCLUSION:

There is a strong association of the occurrence of HO with subsequent loss of movement of the implanted cervical artificial disc. We have found that sex and age are two possible risk factors in the development of HO after cervical disc replacement.

Optimal timing of preoperative radiation for prophylaxis against heterotopic ossification. A rabbit hip model

BACKGROUND

In a previous study, we developed a rabbit model of heterotopic ossification and demonstrated that 800 or 1200 cGy of radiation before an operation on the hip significantly decreased postoperative ectopic bone formation compared with that seen after the operation on the non-irradiated, contralateral hip. The purpose of this study was to determine the optimal preoperative timing of radiation prophylaxis against heterotopic ossification following hip surgery in this same experimental model.

METHODS

Seventy-two hips in thirty-six New Zealand White rabbits were divided into four treatment groups corresponding to four preoperative points in time (four hours, twenty-four hours, seventy-two hours, and three weeks). The hips were irradiated with 1200 cGy at the different preoperative time points (eighteen hips at each time) to investigate the efficacy of the four preoperative radiation protocols. The rabbits then underwent bilateral hip surgery. They were killed and radiographs were made four months postoperatively. Heterotopic ossification was graded according to a modification of the scale of Brooker et al. The mean grade, the interobserver and intraobserver reliability, and the significance (p < 0.05) of the differences between the groups were evaluated.

RESULTS

Radiation delivered at twenty-four hours preoperatively was significantly more effective for prophylaxis against heterotopic ossification than was radiation delivered at four hours or seventy-two hours preoperatively (p < 0.05), and the difference between the twenty-four-hour and three-week groups approached significance (p = 0.088). Furthermore, the twenty-four-hour group had a significantly lower percentage of hips with high-grade heterotopic ossification than did the four-hour (p = 0.02), seventy-two-hour (p = 0.002), and three-week (p = 0.03) groups.

CONCLUSIONS

Preoperative irradiation to prevent heterotopic ossification optimally should be administered twenty-four hours before the operation. This latency period probably allows expression of radiation-induced sublethal mutations in the genetic code of pluripotential stem cells and precludes differentiation to osteoblastic cell lines.

The origin of osteoprogenitor cells responsible for heterotopic ossification following hip surgery: an animal model in the rabbit

PURPOSE

To investigate the source of osteoprogenitor cells responsible for heterotopic ossification (HO) following total hip arthroplasty in an animal model.

METHODS

New Zealand White (NZW) rabbits (n = 20) received a radiation treatment 24 h preoperatively to the hip joint of one hindquarter and to the femoral shaft of the contralateral side. Subjects underwent bilateral hip surgery 24 h after treatment. Subjects were euthanized and radiographed 4 months postoperatively. Heterotopic ossification was graded according to a modified Brooker scale. Mean grade, intra-observer reliability, and statistical significance (p < 0.05) were evaluated to compare the severity of heterotopic ossification between hindquarters treated with hip irradiation versus those treated with femoral shaft irradiation.

RESULTS

The Fleiss Weighted Kappa Statistic indicated "almost perfect" (0.872) intra-rater reliability of radiographic heterotopic ossification grading. The average heterotopic ossification grade for the group receiving radiation to the hip was significantly greater than that for the group receiving radiation to the femoral shaft (2.575 versus 2.0, p < 0.02).

CONCLUSION

Although both have some beneficial effect, our results demonstrate that irradiation of the femoral canal is significantly more effective than irradiation of the hip joint and abductor musculature for heterotopic ossification prophylaxis. This suggests that osteoprogenitor cells responsible for heterotopic ossification originate from both the hip abductors and the femoral canal, but the data provide indirect evidence that the femoral canal may be a more dominant source of these cells in the rabbit model.

Incidence of heterotopic bone formation after major hip surgery

BACKGROUND

Heterotopic bone formation is a well-established complication of major hip surgery, but traditional reviews of the published literature may have underestimated its frequency.

METHODS

A systematic overview of all the relevant studies was performed to determine reliably the incidence of any heterotopic bone formation and the incidence of each Brooker equivalent grade. Separate estimates were made for patients with total hip replacement and patients with acetabular fracture repair.

RESULTS

A computer-based search identified 218 studies with data on the incidence of heterotopic bone formation after either hip replacement or acetabular fracture repair. These studies included data from an estimated 59 121 operated hips among patients that received total hip replacement and an estimated 998 hips among patients that underwent acetabular fracture repair. In these studies, the incidence of any heterotopic bone formation was 43% after total hip replacement and 51% after acetabular fracture repair. The incidence of severe heterotopic bone formation was 9% and 19%, respectively.

CONCLUSIONS

These results suggest that heterotopic bone formation occurs more frequently after total hip replacement than is generally believed. It is possible that heterotopic bone formation is a more important cause of postoperative disability than has previously been recognized and that effective prophylactic regimens might improve outcome in substantial numbers of patients.

Radiation prophylaxis for heterotopic ossification about the hip joint--a multicenter study

PURPOSE

Prophylactic radiotherapy (RT) can prevent ectopic bone formation about the hip after total hip arthroplasty. The German Cooperative Group on Radiotherapy for Benign Diseases conducted a patterns of care study about this indication addressing the involved institutions, RT dose concepts, clinical handling, and treatment outcome of prophylactic RT about the hip joint.

METHODS AND MATERIALS

In 1999, a patterns of care study was conducted in all German institutions to analyze the accrual pattern, number of patients, and different indications for the use and performance of prophylactic RT about the hip. The applied RT concepts of prophylactic RT were evaluated with regard to the RT technique, timing of RT (pre- or postoperative), RT dose prescription (median, range of single and total doses), and treatment outcome. All institutions were asked about the radiologic and functional failure rates at least 1 year after the completion of RT using the established radiologic (Brooker) and functional (Harris) scores with objective and subjective evaluation components.

RESULTS

One hundred fourteen institutions reported their clinical experience with prophylactic RT for the prevention of heterotopic ossification about the hip joint: 70 community hospitals, 23 university hospitals, and 21 private RT practices. In 1999, 5677 patients (5989 hips) had received prophylactic RT. The median number per institution was 36 patients (range 8-240). The interdisciplinary referral included orthopedic surgery (89 institutions; 3763 patients), trauma surgery (82 institutions; 1611 patients), or other disciplines (8 institutions; 298 patients). Preoperative RT was applied in 53 institutions 0.5-24 h before surgery, and postoperative RT was applied in 54 institutions 1-120 h after surgery. Most patients received 1 x 7 Gy either pre- or postoperatively. The total dose range was 5-10 Gy (preoperative RT) or 5-16 Gy (postoperative RT); the median total RT dose of both RT concepts was 7 Gy. Cobalt-60 (n = 15), linear accelerators (n = 95), and a few lower energy units (n = 4) were used. Bony structures or prostheses were shielded with standard blocks in 31 and with individual blocks in 27 institutions. Long-term clinical evaluation was available in 30 institutions from 4377 hips. Of those, 475 (11%) developed radiologic failures according to Brooker's criteria. Functional hip evaluation was available in 5 institutions from 685 hips. Of those, 34 (5%) had functional failures according to the criteria of Harris. No difference in outcome was found between pre- and postoperative RT, but was with regard to the patient's referral and the timing of RT. The patients who were treated >8 h before surgery or >72 h after surgery experienced a higher radiologic failure rate; radiologic failures were an important precondition for functional failures (p <0.05).

CONCLUSION

This patterns of care study comprises the largest number of cases reported for prophylactic hip RT to date. The results reveal that both preoperative (within 24 h) and postoperative RT (within 72 h) are effective in preventing heterotopic ossification after hip surgery. Both RT concepts achieved a similar low radiologic and functional failure rate. Single-dose RT concepts, especially, can be recommended as an excellent treatment alternative for patients with contraindications to long-term steroid or nonsteroidal anti-inflammatory agents, and this approach has become standard in most German RT institutions.

Radiation therapy for heterotopic ossification

Heterotopic ossification is a common complication after bone and joint surgery. If the disease progresses, it may cause pain and disability, eventually defeating the purpose of surgery in the first place. Today, prophylactic treatment is indicated after surgery. Both nonsteroidal antiinflammatory drugs and radiation therapy are effective. Radiation therapy is associated with fewer side effects and is preferred. Single-dose postoperative irradiation has been found to be as effective as fractionated radiation therapy.

The suppression of heterotopic ossifications: radiation versus NSAID therapy--a prospective study

This prospective, randomized study compares the effect of postoperative irradiation and nonsteroidal anti-inflammatory drug (NSAID) therapy on the prevention of heterotopic ossifications after the implantation of a total hip endoprosthesis. A total of 154 operations were performed; one group of patients underwent radiation treatment of 3 x 3.3 Gy, and the other group took 3 x 50 mg of diclofenac per day over a period of 3 weeks. Average age, sex, preoperative diagnosis, and risk factors were similar in both groups. Postoperative radiation began on average 2.9 days after operation, and the radiation therapy was finished on average within 3.8 days. NSAID prophylaxis was begun on the first postoperative day. Heterotopic ossifications occurred in two of the patients who had undergone postoperative prophylaxis by radiation. In both cases, the ossification was Brooker I, and there was no functional impairment. There were no ossifications of Brooker II-IV in this group. One patient had a Staphylococcus epidermidis infection, and fistula revision had to be carried out; the prosthesis could be left in place. In the group treated with NSAID, 16 heterotopic ossifications stage Brooker I and 2 stage Brooker II could be detected. Eleven patients stopped the treatment because of gastrointestinal problems. Both postoperative radiation and NSAID therapy have proved to be effective prophylactic methods. In direct comparison, radiation prophylaxis by 3 x 3.3 Gy proved to be slightly more successful than NSAID prophylaxis.

The Frank Stinchfield Award. Inhibition of heterotopic ossification with radiation therapy in an animal model

An animal model for the study of heterotopic ossification was developed and the effects of perioperative radiation were analyzed. In Phase I, New Zealand White rabbits (n = 18) underwent surgery either with or without muscle injury on each hip to establish the most reliable model in which to study heterotopic ossification. In Phase II, rabbits (n = 36) underwent either 400, 800, or 1200 cGy radiation to one hip 24 hours after bilateral hip surgery to establish a dose response relationship for postoperative radiation therapy. In Phase III, rabbits (n = 24) underwent preoperative radiation therapy (800 cGy) at 4, 16, or 24 hours preoperatively to investigate the mechanism of action and efficacy of preoperative radiation therapy. Monthly radiographs were graded by blinded observers for severity of heterotopic ossification. Mean grade, intraobserver and interobserver variability, and statistical significance were evaluated. In Phase II, 17 of 18 rabbits generated heterotopic ossification in both hips, and the mean grade of heterotopic ossification was always greater on the operative side with intentional muscle injury. Variability in the grading was considered excellent. Phase II revealed that 800 cGy was the minimal effective dose. Contrary to hypothesis, Phase III revealed an increasing grade of heterotopic ossification coinciding with a decreasing preoperative time interval, with the difference in heterotopic ossification grade with 24-hour versus 4-hour preoperative radiation being significant. The rabbit model is reliable and reproducible and closely resembles the human clinical situation after hip surgery. Preoperative and postoperative radiation effectively prevented heterotopic ossification formation. The results support the use of preoperative radiation and establish a need for additional investigation regarding the mechanism of action and timing of preoperative radiation therapy.

Prevention of heterotopic ossification about the hip: final results of two randomized trials in 410 patients using either preoperative or postoperative radiation therapy

PURPOSE

Experimental and clinical data support effectiveness of perioperative radiotherapy to prevent heterotopic ossification after hip surgery or trauma. Since 1987, two prospectively randomized trials were performed in patients with high-risk factors to develop heterotopic ossification: the first (HOP 1) to assess the prophylactic efficacy of postoperative low vs. medium dose radiotherapy, and the second (HOP 2) to assess the prophylactic efficacy of pre vs. postoperative radiotherapy.

METHODS AND MATERIAL

410 patients with high risk to develop heterotopic ossifications about the hip following hip surgery were recruited. Between June 1987 and June 1992, 249 patients were randomized in HOP 1 to postoperative "low dose" (5 x 2 Gy; total: 10 Gy) or "medium dose" (5 x 3.5 Gy; total: 17.5 Gy) radiotherapy. Between July 1992 and December 1995, 161 patients were randomized in HOP 2 to either 1 x 7 Gy preoperatively (< or = 4 h before surgery) or 5 x 3.5 Gy (total: 17.5 Gy) postoperatively (< or = 96 h after surgery). With exception of age and type of implant (cemented vs. uncemented prosthesis) all confounding patient variables (gender, prior surgery) and predisposing risk factors were similarly distributed between both trials and treatment arms. Portals encompassed the periacetabular and intertrochanteric soft tissues. Radiographs were obtained prior and immediately after surgery and at least 6 months after surgery to assess the extent of ectopic bone formation about the hip. Modified Brooker grading was used to score the extent of heterotopic ossification. Harris scoring was applied to evaluate the functional hip status. If the scores decreased from immediate post or preoperative status, respectively, to the last follow-up, radiological or functional failures were assumed.

RESULTS

Effective prophylaxis was achieved in 227 (91%) hips of HOP 1 and in 142 (88%) of HOP 2. In HOP 1, 15 (11%) radiological failures were observed in the low-dose group compared to 7 (6%) in the medium dose group (p > 0.05). In HOP 2, 4 (5%) radiological failures were observed in the postoperative and 11 (19%) in the preoperative group (p < 0.05). Subgroup analysis of the preoperative group revealed that the highest failure rate occurred in patients with prophylactic radiotherapy prior to removal of ipsilateral Brooker Grade III and IV ossification (39%) (p < 0.001), while all other patients in the preoperative group had a failure rate that was comparable to postoperative treatment groups. In multivariate logistic regression analysis the number of high-risk factors for development of heterotopic ossification (p = 0.03) and the time to RT initiation (p = 0.05) were independent prognostic factors in the HOP 1 study. For the HOP 2 study, the multivariate logistic regression analysis revealed the number of high-risk factors for development of heterotopic ossification (p = 0.003), the preoperative HO grade (p = 0.001) and the RT dose concept (p = 0.05) as independent prognostic factors. Other factors including type of implant (cemented vs. uncemented) did not affect the prophylactic efficacy of radiotherapy. There were no increased intra- and postoperative complications seen in the preoperative group, and no long-term complications were observed in both HOP studies. For functional failures (decrease of Harris score) no statistically prognostic factors were found. There were less functional failures in HOP 1 (18 = 7%) than in HOP 2 (23 = 14%, but this difference was not statistically significant. Only patients with high Brooker Grade III and IV at last FU achieved a lower Harris score than those with low Brooker Grade 0, I and II (p < 0.05).

CONCLUSION

With the exception of a small subgroup of patients with ipsilateral high Brooker Grade III and IV, pre- and postoperative radiotherapy are equally effective to prevent heterotopic ossification about the hip after hip surgery and total hip arthroplasty. Fractionated medium dose radiotherapy resulted in the low

Preoperative irradiation for prevention of heterotopic ossification following total hip arthroplasty

Eighty-six hips in eighty-five patients who were considered to be at risk for heterotopic ossification following a total hip arthroplasty were prospectively randomized or assigned to one of two treatment groups that received a single 800-centigray dose of limited-field radiation either preoperatively (Group I) or postoperatively (Group II). The risk factors for postoperative heterotopic ossification included previous heterotopic ossification following an operation about the hip, hypertrophic osteoarthrosis or post-traumatic osteoarthrosis characterized by the presence of extensive osteophytes, radiographic evidence of diffuse idiopathic skeletal hyperostosis, and ankylosing spondylitis. The hips in Group I were irradiated within 6.1 hours before the operation and those in Group II, within 51.3 hours after the operation. Either extra-field ossification or heterotopic ossification was observed in forty-one (48 per cent) of the eighty-six hips, thereby confirming the high risk for the population in this study. After a minimum duration of follow-up of six months, thirty-seven (76 per cent) of the forty-nine hips that had been treated with preoperative irradiation exhibited no new heterotopic ossification and eleven, progression to grade-I or II ossification. The remaining hip in that group was in a woman who had Paget disease as well as previous grade-IV (ankylosing) heterotopic ossification about the ipsilateral hip; heterotopic ossification progressed from grade II on the radiographs made immediately after the index revision procedure to grade III at the most recent follow-up assessment. Of the thirty-seven hips that had been treated with postoperative irradiation, twenty-seven (73 per cent) exhibited no new heterotopic ossification and nine had progression from grade-0 to grade-I ossification. The remaining hip in that group was in a man who had Parkinson disease and previous grade-III ossification about the ipsilateral hip; heterotopic ossification progressed from grade III immediately post-operatively to grade IV at the time of the most recent evaluation. Extra-field ossification was identified in twelve (24 per cent) of the forty-nine hips that had been irradiated preoperatively compared with three (8 per cent) of the thirty-seven hips that had been irradiated postoperatively (p = 0.05). Extra-field ossification was not associated with clinical symptoms of bursitis of the greater trochanter in any hip. Three of the ten hips that had a revision operation subsequently had a non-union of the greater trochanter; all three had been treated with preoperative irradiation. The findings of the present study suggest that pre-operative irradiation is effective for the prevention of heterotopic ossification following total hip arthroplasty and that it eliminates the discomfort and morbidity that are associated with conventional postoperative treatment. Furthermore, the efficacy of preoperative irradiation suggests that osteogenic precursor cells that are active in this process are derived from the local tissues within the operative field rather than from distant blood-borne cell lines.

Heterotopic ossification

Heterotopic ossification is a well-recognized condition frequently encountered by the orthopedic surgeon. Although typically asymptomatic, heterotopic ossification can be a complication of extreme severity. This article is a review of literature and attempts to clarify the definition, and delineates the etiology, incidence, risk factors, and current modes of prophylaxis and treatment of various types of heterotopic ossification.

Heterotopic bone formation affecting the hip joint is preventable in high risk patients by post-operative radiation

Between 1984 and 1993, 40 high risk patients (45 hips) received postoperative irradiation as prophylaxis against heterotopic ossification (HO). Radiotherapy was commenced within 5 days of the surgery in 43 of 45 hips. The development of HO was assessed by comparison of radiographic films prior to irradiation and at least 2 months after treatment (median interval 12 months). Progression of HO was observed in only two of 45 hips (4.3%) and of clinical significance in one (2.2%). Treatment was well tolerated with no acute complications or loosening of prosthetic components attributable to irradiation. During the study period, the treatment programme changed from 20 Gy in 10 fractions to 6-8 Gy in a single fraction, without loss of treatment efficacy. As well as improving resource utilization, single fraction techniques allow fewer patient transfers thereby reducing patient discomfort and risk of hip dislocation. This procedure is uncomplicated and should be considered more widely in the management of this disabling non-malignant condition.

Heterotopic ossification following primary total knee arthroplasty

Ninety-eight consecutive primary total knee arthroplasties (TKAs) in 70 patients were retrospectively evaluated for heterotopic ossification (HO). A radiographic classification was devised based on the extent and location of the ectopic bone. Twenty-five knees (26%) in 19 patients developed HO. Eight of 11 patients (73%) with preexisting heterotopic bone at other sites developed HO in the index knee. Multivariate analysis demonstrated that advanced HO was associated with restricted knee motion. Eight knees with advanced HO had a mean 14 degrees decrease in postoperative, as compared with preoperative, knee flexion (P < .05). For all patients with HO, mean lumbar spine bone mineral density (BMD) was significantly elevated compared with a matched control group not developing HO (P < .05). Heterotopic ossification following primary TKA correlates with a limitation of postoperative knee flexion and is predicted by increased lumbar BMD. Preoperative measurement of spinal BMD may identify those patients at risk for HO and allow for the institution of preoperative prophylaxis and modification of postoperative rehabilitation to optimize functional outcome following TKA.

Single-dose irradiation for the prevention of heterotopic ossification after total hip arthroplasty. A comparison of doses of five hundred and fifty and seven hundred centigray

One hundred and seven hips (ninety-four patients) that had risk factors associated with the development of heterotopic ossification after total hip arthroplasty were treated with a single dose of radiation after the operation in an attempt to prevent the formation of heterotopic bone. A study was conducted to compare the efficacy of a single dose of 550 centigray (nineteen hips) with that of a single dose of 700 centigray (eighty-eight hips). Heterotopic ossification developed in twelve (63 per cent) of the nineteen hips that were treated with 550 centigray; grades 1, 2, and 3, according to the classification of Brooker et al., developed in four hips each. Two of the patients who received 550 centigray were symptomatic. Heterotopic ossification developed in nine (10 per cent) of the eighty-eight hips that were treated with 700 centigray; the lesion was grade 1 in six, grade 2 in one, and grade 3 in two. None of the patients who received 700 centigray were symptomatic. We concluded that single-dose irradiation consisting of 550 centigray is inadequate for the prevention of heterotopic ossification in high-risk patients after total hip arthroplasty. We recommend a dose of 700 centigray as effective prophylaxis for these patients.

Preoperative versus postoperative radiotherapy for prevention of heterotopic ossification (HO): first results of a randomized trial in high-risk patients

PURPOSE

In vivo data support the effectiveness of pre- and postoperative radiotherapy in suppressing the development of heterotopic ossification after hip surgery. In June 1992 a prospectively randomized trial was initiated to assess the comparative efficacy of pre- vs. postoperative prophylactic radiotherapy in patients with high risk to develop heterotopic ossification after hip surgery.

METHODS AND MATERIAL

Between June 1992 and September 1993 a total of 84 eligible patients with high risk profile for the development of heterotopic ossification were entered in the study. They were randomized to receive radiotherapy either preoperatively (< 4 h before surgery) or according to a "standard protocol" postoperatively (< 72 h after surgery). A single 7 Gy fraction was administered to the preoperative group, while the postoperative group received a previously tested scheme of five fractions of 3.5 Gy (total dose 17.5 Gy). The treatment portal encompassed the soft tissues between the periacetabular region of the pelvis and the intertrochanteric portion of the femur. Important patient variables (age, sex, prior surgery) and predisposing risk factors were equally distributed between both treatment arms. X rays of the irradiated hips were obtained prior and immediately after surgery as well as at 6 months after surgery. The modified Brooker grading was used to score the extent of heterotopic ossification. The Harris score was applied to judge the overall functional status of the hip. If the Brooker grade and Harris score decreased from the immediate postoperative or preoperative status respectively to the follow-up situation, the case was considered as a "treatment failure."

RESULTS

At a minimum 6 months follow-up after hip surgery 44 patients were available for evaluation. Effective prophylaxis was achieved in 41 (93%) hips. Two "radiological failures" were observed in the preoperative group and one in the postoperative group. Neither the pre- nor the postoperative interval affected the prophylactic efficacy. There were no increased intra- and postoperative complications seen in the preoperative group. The interval of partial strain (50% body weight) to the operated hip was longer in the preoperative group (19 days +/- 27) as compared to the postoperative group (8 days +/- 13), however the interval to full strain (100% body weight) was equal in both groups. The functional status (Harris Score change) of the operated hip decreased only in two (5%) patients ("functional failures"). The overall change was better in the postoperative group (42.7 +/- 17.1) as compared to the preoperative group (34.3 +/- 13.7) (p = 0.08, NS) as well as with regard to the criteria "limp" (p = 0.05) and "use of walking support" (p = 0.10, NS). In in all other aspects no differences were observed between both treatment arms. Therefore, the preliminary results for preoperative radiotherapy are similar to historical results obtained with postoperative radiotherapy regimens.

CONCLUSION

Preoperative radiotherapy of the operative site applied within 4 h prior to elective hip surgery and total hip arthroplasty appears to be equally effective to currently accepted postoperative radiotherapy regimens in prevention of clinically significant heterotopic ossification about the hip. Improved patient comfort, ease of treatment management, and avoidance of possible postoperative complications associated with moving and positioning the patient in the immediate postoperative period are the major advantages of the preoperative radiotherapy concept.

Randomized trial comparing preoperative versus postoperative irradiation for prevention of heterotopic ossification following prosthetic total hip replacement: preliminary results

PURPOSE

Previous in vivo data support effectiveness of preoperative irradiation in suppressing heterotopic ossification (HTO) in a rat model. A prospectively randomized, multiinstitution clinical trial to assess the comparative efficacy of preoperative vs. postoperative irradiation in preventing HTO in total hip replacement patients was undertaken.

METHODS AND MATERIALS

One hundred and twenty-two patients (124 hips) with significant risk factors for HTO following elective total hip replacement were randomized to receive irradiation via either preoperative (< 4 h before surgery) or "standard" postoperative (< 48 h after surgery) schedules. Single 7-8 Gy fractions were administered. Treatment volume included soft tissues between periacetabular region of pelvis and intertrochanteric portion of femur. All but nine patients had biologic fixation prostheses, the porous-coated portions of which were shielded. Radiographs of treated hips were obtained immediately and at 2 and 6 months postsurgery. Heterotopic ossification was scored according to the Brooker Grading system.

RESULTS

Ninety-eight patients are evaluable (55 preoperative, 43 postoperative) with median follow-up of 38 weeks. No significant differences were noted in the incidence of overall HTO (26% preoperative vs. 28% postoperative, p = 1.0) or clinically significant Brooker grade 3 or 4 HTO (2% preoperative vs. 5% postoperative, p = 0.58). No significant differences in treatment variables (including time interval between preoperative irradiation and surgery) were evident on comparing preoperatively treated patients forming HTO with those who did not.

CONCLUSION

Prophylactic irradiation of the operative site within 4 h prior to elective total hip replacement appears to be comparably effective to the currently accepted postoperative treatment schedules in prevention of clinically significant HTO about the hip. This finding is of importance in terms of patient comfort, ease of treatment, and avoidance of possible complications associated with moving the patient to the radiotherapy department in the immediate postoperative period.

Heterotopic ossification: a review of symptoms and treatment

Heterotopic ossification (HO) is the abnormal development of bone tissue within soft tissue. Its etiology and pathology are uncertain. This condition is often seen near one or more joints in people who have sustained traumatic injuries of varying types. Symptoms include localized swelling, pain, increase in temperature, and loss of the joint's range of motion at the affected site. Further testing generally reveals an increase in serum alkaline phosphatase, a positive three-phase bone scan, and the identification of bone formation on radiographs. A review of the literature reveals that common treatment options include range-of-motion exercises to maintain joint function, pharmacologic intervention, possible irradiation of the site, and surgical removal of ankylosing bone. The rehabilitation nurse must be aware of this medical complication to participate in its identification and treatment, as well as to be effective in counseling and educating patients and their families.

Heterotopic ossification in total hip arthroplasty. The influence of the approach

The effects of lateral approaches for total hip arthroplasty on heterotopic bone formation were studied in 264 patients with primary osteoarthritis. The Hardinge approach was used in 82 patients, the transtrochanteric approach in 94, and the Liverpool approach in 88. The incidence of heterotopic ossification was 42%. A severe form of bone formation occurred five times more in the Liverpool approach than in other two approaches.

Ectopic ossification in hip arthroplasty. A retrospective study of predisposing factors in 637 cases

We investigated predisposing factors for the development of heterotopic ossification in a retrospective study of 637 hip arthroplasties, of which 484 were unilateral, 62 bilateral and 29 revision operations. The frequency of heterotopic ossification after a primary hip arthroplasty was 57 percent. In a univariate analysis, men, patients with hypertrophic arthrosis, and cemented arthroplasty were all at risk of developing heterotopic ossification. After a multivariate analysis, the male sex and the cemented arthroplasty remained as significant factors. In bilateral operations, the contralateral side developed heterotopic ossification in 82 percent when the primary hip operation had already caused ossification. There was no increase in ossifications after the contralateral operation. Half of the revision operations had an increase of heterotopic ossification from 1 to 4 Brooker classes.

Prevention of heterotopic ossification (HO) after total hip replacement: randomized high versus low dose radiotherapy

In a prospectively randomized study 60 hips at high risk for heterotopic ossification (HO) received prophylactic radiotherapy (RT). Randomization was performed between a low dose (LD-RT) of 5 x 2 Gy (arm A: 32 patients) and a high dose (HD-RT) of either 10 x 2 Gy (arm B1; 8 patients) or 5 x 3.5 Gy (arm B2; 20 patients). Relevant patient and risk factors were equally distributed in both treatment arms. 4 (7%) patients developed treatment failures. A short delay of RT after postoperative day (POD) 4 was significantly correlated with failure (p < 0.001). The results suggest no difference in prophylactic efficacy between LD-RT and HD-RT treatment. 2/19 (11%) patients receiving additional diphosphonates and 2/18 (11%) on no medication failed RT treatment, but none on indomethacin did so. In conclusion, immediate postoperative RT has been shown to be an effective prophylactic treatment.

Erosion and heterotopic bone formation after alloplastic temporomandibular joint reconstruction

Twenty-three temporomandibular joint arthroplasties using metallic condylar prostheses were performed because of severe ankylosis (8 patients), segmental mandibular resections in tumor surgery (9 patients), and after extensive trauma (2 patients). A clinical and radiological follow-up study showed heterotopic bone formation in 52% of cases and glenoid fossa resorption in 43%. In one patient with rheumatoid arthritis the condyle eroded through the skull base 10 months after surgery. Seven prostheses (30%) were removed and/or exchanged during the average 27.6-month follow-up.

Naproxen prevention of heterotopic ossification after hip arthroplasty. A prospective control study of 55 patients

The effect of naproxen on heterotopic ossification after total hip replacement was studied in a randomized, double-blind trial. Twenty-eight patients received 250 mg naproxen thrice daily for 4 weeks postoperatively starting on the morning of the operation while 27 control patients received a placebo. Three months after the operation, 13 patients in the control group had heterotopic ossification compared with 4 patients in the group that received naproxen; and after 1 year, the figures were 15 and 4, respectively (P less than 0.01). Three control patients had severe ossifications. We conclude that naproxen given for 4 weeks is sufficient to decrease the incidence of heterotopic ossification after cemented total hip replacement.

Heterotopic bone formation after total hip arthroplasty in patients with primary or secondary coxarthrosis

Heterotopic bone formation was investigated in 392 Charnley low-friction total hip arthroplasties. A multivariate linear regression analysis was used to account for the influence of co-variables: sex, age at surgery, postoperative treatment with antiinflammatory drugs during at least the first 2 weeks, and previous ipsilateral hip surgery. A total of 232 hips had been treated for primary coxarthrosis, and 114 and 46 hips for secondary coxarthrosis due to congenital dislocation and fracture-dislocation of the hip, respectively. None of the hips with primary coxarthrosis previously had ipsilateral hip surgery, whereas 41 hips (36%) in patients with congenital dislocation of the hip and 28 hips (61%) in patients with fracture-dislocation of the hip had one or more ipsilateral surgical procedures prior to the arthroplasty. The sex ratio varied between the groups, with a male:female hip ratio of 1:1, 1:10, and 3:1 for the three groups, respectively. The risk of developing grades 2 or 3 heterotopic ossification after total hip arthroplasty were significantly higher in men, patients without postoperative treatment with antiinflammatory drugs, and patients above age 60. In contrast, the analysis documented that previous ipsilateral hip surgery and type of coxarthrosis did not influence lesion development, supporting the theory that a systemic, rather than local factor, is responsible for the development of heterotopic bone formation after total hip arthroplasty.