Long-term follow-up results of primary and recurrent pigmented villonodular synovitis.

OBJECTIVE: Adequate documentation of the outcome of treatment of pigmented villonodular synovitis (PVNS) is sparse. Available case series show relatively short follow-up times and often combine locations or subtypes to increase patient numbers. This article describes the long-term follow-up of a single institution's large consecutive series of PVNS. METHODS: Retrospectively, 107 PVNS patients were identified between 1985 and 2011 by searching pathology and radiology records. Treatment complications, recurrences and quality of life were evaluated. Most patients (85.2%) were primarily or secondarily treated at our institution. RESULTS: Both subtypes, localized PVNS [29 (27%)] and diffuse PVNS [75 (70%)] were represented. The knee was affected in 88% of patients. Treatments received were surgery, external beam radiotherapy, radiosynovectomy, targeted therapy, immunotherapy or combinations of these. Forty-nine (46%) patients had prior treatment elsewhere. The mean follow-up from diagnosis until last contact was 7.0 years (range 0.3-27.4) for localized PVNS and 14.5 years (range 1.1-48.7) for diffuse PVNS. The 1- and 5-year recurrence-free survival rates for diffuse PVNS were 69% and 32%, respectively. Quality of life, estimated by 36-item Short Form Health Survey (SF-36) scores, were not significantly different between localized and diffuse PVNS. However, both patient groups scored lower than the general population norms on the general health component (59.2 and 56.3, respectively, P < 0.05). CONCLUSION: Recurrence rates of PVNS increase with time. Long-term follow-up shows, particularly in diffuse PVNS, it is a continually recurring problem, and over time it becomes increasingly difficult to cure. The quality of life is decreased in patients with PVNS compared with the general population.

Pigmented villonodular synovitis: current concepts about diagnosis and management.

At present, the treatment strategies in patients with localized and diffuse forms of pigmented villonodular synovitis have more or less been standardized. However, these strategies are not optimal because high recurrence rates persist and studies with a sufficient level of evidence are lacking. This systematic review article describes all known treatment options for intra-articular pigmented villonodular synovitis and their clinical results. Based on this research, we provide guidelines to support physicians in making the optimal treatment decisions. Given the rarity of the disease, randomized studies are not to be expected, but an international registry through existing networks would offer the benefit of getting a better insight into the outcome of this disease. Therefore, we propose a basic set of data to be investigated and ideally to be reported on in such a registry.

Long-term results of cemented total hip arthroplasty in patients younger than 30 years and the outcome of subsequent revisions.

BACKGROUND: The number of total hip arthroplasties in patients under 30 years is increasing over the years. Almost all of them will face at least one or more future revisions in their life. Therefore, the implant used should have a high survival rate, and needs to be easily revisable resulting in a low re-revision rate. Several studies have evaluated the outcome of total hip arthroplasties in patients under 30 years. However, only a few reported on the follow-up outcome of 10 years or more. In addition, none of these reports published data of the subsequent revisions of these implants within their original report. METHODS: We studied historically prospective collected data of 48 consecutive patients (69 hips) younger than 30 years, treated with a cemented primary total hip prosthesis between 1988 and 2004. Since the last evaluation of this cohort, two patients were lost to follow-up. For all hip revisions in this cohort, again cemented implants were used, mostly in combination with bone impaction grafting. Kaplan-Meier survival curves at 10- and 15 years for the primary total hip arthroplasties and revisions were determined. RESULTS: The mean age at time of primary surgery was 25 years (range, 16 to 29 years). Mean follow-up of the primary hips was 11.5 years (range, 7 to 23 years). During follow-up 13 revisions were performed; in 3 cases a two-stage total revision was performed for septic loosening and 9 cups were revised for aseptic loosening. There were no aseptic stem revisions. The 10 and 15-year survival rates with endpoint revision for aseptic loosening of the primary total hip were 90% (95% CI: 79 to 96) and 82% (95% CI: 65 to 92) respectively. None of our 13 subsequent revisions needed a re-revision within 10 years after re-implantation. CONCLUSIONS: Cemented total hip implants in patients under 30 years have an encouraging outcome at 10 and 15 years after surgery in these young patients. The 13 revised hips, treated with bone grafting and the third generation cement technique, were performing well with no re-revisions within ten years after surgery.

High fatigue scores before and after surgical treatment of bone and soft tissue tumors.

The first objective of the present study was to investigate fatigue severity in patients diagnosed with bone and soft tissue tumors prior to the surgical treatment of the tumor and 6 months post-operatively. The second objective was to determine which variables are associated with severe fatigue. Patients diagnosed with benign or low-grade malignant bone and soft tissue tumors, undergoing surgical therapy for the tumor only, were included in this study. The control group contained patients scheduled for knee arthroscopy for suspected meniscus tears. Fatigue, pain, anxiety and self-efficacy were measured pre-operatively and after 6 months and each patient wore an actometer to quantify physical activity. In the tumor group of 43 patients, 35% were severely fatigued pre-operatively and 33% post-operatively. The tumor group reported a significantly higher level of anxiety. No differences were observed in pain, physical limitations, self-efficacy or actometer scores. Multiple regression analysis of the tumor group revealed that higher pain scores, higher state anxiety and lower self-efficacy were asssociated with fatigue severity. In the control group of 24 knee arthroscopy patients, the percentage of severely fatigued patients decreased from 38% (n=9) prior to treatment to 29% (n=7) 6 months later. A substantial number of patients were severely fatigued in both the tumor group and the knee arthroscopy group. Self-efficacy, pain and anxiety appear to be the most important variables associated with fatigue severity in tumor patients prior to surgery.

[Hip resurfacing in patients under 55 years of age]. / De resurfacing heupprothese bij patiënten jonger dan 55 jaar.

Hip resurfacing arthroplasty was introduced as an alternative to the conventional total hip arthroplasty which had shown suboptimal results in younger patients. Application of the resurfacing technique in younger patients has increased over the last few years. To date, no randomized controlled trials with a minimum follow-up span of 10 years comparing hip resurfacing to conventional hip replacement have been conducted in patients under 55 years of age. Australian and English hip registries demonstrate high revision rates after 5 years for some brands of resurfacing implants. In addition to these disappointing revision rates, the complication of aseptic lymphocytic vasculitis caused by metal particles evoking a local tissue reaction has been increasingly reported. The resurfacing procedure recently received some negative media attention in the Netherlands, leading to confusion among patients. In order to ease patient doubts, it is important to correctly inform them as to the type of implant used, for example, by means of the website or an information card.

Total hip arthroplasties in young patients under 50 years: limited evidence for current trends. A descriptive literature review.

We examined all reported outcomes of uncemented and cemented total hip arthroplasty in patients younger than 50 years of age listed in Medline (1966- 1 January 2009) and PubMed, and scrutinised reference lists of relevant papers. In addition, we evaluated relevant data in the Swedish hip arthroplasty register. 109 relevant articles were identified, 37 of which had a mean follow-up longer than 10 years. Although uncemented implants are widely used in patients under 50 years of age, there are only 2 reports that fulfil the criteria published by the National Institute for Clinical Excellence (NICE) in the United Kingdom (follow-up of >10 yrs and survival of =90%). Current trends relating to implant selection remain unsupported by survival data, and additional information about the long-term results of newer implants is essential. As matters stand, the most reliable results relate to cemented implants.

Percutaneous radiofrequency ablation of osteoid osteomas with use of real-time needle guidance for accurate needle placement: a pilot study.

PURPOSE: To evaluate the accuracy and technical success of positioning a radiofrequency ablation (RFA) electrode in osteoid osteomas by use of a new real-time needle guidance technology combining cone-beam computed tomography (CT) and fluoroscopy. MATERIALS AND METHODS: Percutaneous RFA of osteoid osteomas was performed in five patients (median age 18 years), under general anesthesia, with the use of cone-beam CT and fluoroscopic guidance for electrode positioning. The outcome parameters were technical success, meaning correct needle placement in the nidus; accuracy defined as the deviation (in mm) from the center of the nidus; and clinical outcome at follow-up. RESULTS: In all five cases, positioning was possible within 3 mm of the determined target location (median nidus size 6.8 mm; range 5-10.2 mm). All procedures were technically successful. All patients were free of pain at clinical follow-up. No complications were observed. CONCLUSION: Real-time fluoroscopy needle guidance based on cone-beam CT is a useful tool to accurately position radiofrequency needles for minimally invasive treatment of osteoid osteomas.

[Total hip arthroplasty in patients under 40 years of age and, if indicated, reconstruction of acetabular defects with bone impaction grafting]. / Totaleheupprothesen bij patiënten jonger dan 40 jaar en reconstructie van botdefecten met botsnippers.

OBJECTIVE: To determine the long-term results of primary cemented total hip arthroplasty in patients under the age of 40. In cases of acetabular defects, initial reconstruction with bone impaction grafting was performed. DESIGN: Cohort analysis. METHODS: Details of patients under the age of 40 who underwent primary cemented total hip arthroplasty between 1 January 1988 and 30 June 2004 were analysed. The primary goal of this study was to determine the time until revision surgery. Kaplan Meier analysis was used to calculate prosthesis survival. RESULTS: A total of 175 total hip arthroplasties in 130 patients were included in the study. Acetabular reconstruction using bone impaction grafting was performed on 84 hips (48%). The average age at surgery was 31 years. Six patients (8 hips) died during follow-up; none of these had undergone revision surgery. Average follow-up was 8.1 years (range: 2.0-18.5). In total, 24 hips (14%) were revised. Reasons for revision were: septic loosening (n = 8), recurrent dislocations (n = 4), traumatic loosening (n = 1) and aseptic loosening (n = 11). The 10-year prosthesis survival was 83% (95% CI: 76-90) with the endpoint 'revision for any reason' and 92% (95% CI: 86-98) with the endpoint 'revision for aseptic loosening'. Aseptic survival of the cups with and without bone impaction grafting was 95% (95% CI: 89-100) and 90% (95% CI: 81-99) (p = 0.73), respectively. CONCLUSION: Hip replacement with cemented total hip arthroplasty in patients under the age of 40 produced good long-term results. Acetabular deficiencies reconstructed with bone impaction grafting also produced good results in this group of patients.

Methodological systematic review: mortality in elderly patients with cervical spine injury: a critical appraisal of the reporting of baseline characteristics, follow-up, cause of death, and analysis of risk factors.

STUDY DESIGN: Methodologic systematic review. OBJECTIVE: To determine the validity of reported risk factors for mortality in elderly patients with cervical spine injury. SUMMARY OF BACKGROUND DATA: In elderly patients with cervical spine injury, mortality has frequently been associated with the type of treatment. To date, however, no review evaluating the validity of reported risk factors for mortality in elderly patients with cervical spine injury has been published. METHODS: Studies evaluating the treatment of cervical spine injuries in elderly (>/=60 years of age) patients were searched through the Medline and EMBASE databases. In addition to standard methodologic details, reporting of putative confounding baseline characteristics and analysis of risk factors for mortality were appraised critically. For this purpose, patient data presented in included studies were pooled. Exploratory descriptive statistics were used for data analysis. RESULTS: Twenty-six eligible studies were identified, including a total of 1550 pooled elderly subjects. Except for 2, all studies reported presence or absence of spinal cord injury. Details concerning the severity and/or extent of the injury were reported in 12 (46%) studies. Pre-existing comorbidities were reported in 9 studies (35%). In the pooled subjects, the cause of death was not reported in 155 of 335 deceased patients (42%). Based on own results, 18 (69%) studies reported on risk factors for mortality. Of these studies, 6 (23%) performed statistical analyses of risk factors for mortality outcomes. Only 1 study statistically adjusted potential risk factors for mortality for confounding. CONCLUSION: Overall, pre-existing comorbidities, concomitant injuries, follow-up and cause of death have been underreported in studies investigating the treatment of cervical spine injuries in elderly patients. To strengthen the validity of risk factors for mortality in future clinical trials, adjustments for appropriately reported putative confounders by regression analysis are mandatory.

Good results with cemented total hip arthroplasty in patients between 40 and 50 years of age.

BACKGROUND AND PURPOSE: Total hip arthroplasties in young patients have lower long-term survival rates than in older patients. We evaluated the use of a unique treatment protocol in patients aged between 40 and 50 years. In all cases we used a cemented THA, and for acetabular deficiencies we also used impacted bone grafts together with a cemented cup. METHODS: In 140 consecutive patients who were between 40 and 50 years of age at index surgery, 168 cemented total hip prostheses were evaluated after a mean follow-up time of 10 (2-19) years. Acetabular deficiencies were reconstructed with wire meshes and impacted bone grafts with a cemented cup (70 hips). During follow-up, 18 patients died (27 hips); in this group 3 hips (3 patients) had been revised. None of the patients were lost to follow-up. In all surviving patients, clinical assessment was performed with hip-score questions and all radiographs were evaluated. RESULTS: All clinical questionnaires showed an improved clinical hip score. 29 hips (17%) were revised after a mean of 8 (0.3-18) years. Kaplan-Meier survival analysis showed a survival of 88% (95% CI: 82-94) after 10 years with revision of either component for any reason. Survival with endpoint revision for aseptic loosening of either component was 94% (95% CI: 90-99) after 10 years. INTERPRETATION: Cemented implants in young patients have satisfying long-term results. Reconstruction of acetabular deficiencies with impacted bone grafts show promising results.

Metastatic potential of an aneurysmal bone cyst.

Aneurysmal bone cysts (ABCs) are benign bone tumors consisting of blood-filled cavities lined by connective tissue septa. Recently, the hypothesis that ABCs are lesions reactive to local hemodynamics has been challenged after the discovery of specific recurrent chromosomal abnormalities. Multiple cases of malignant transformation of ABC into (osteo)sarcoma have been described, as well as a number of cases of telangiectatic osteosarcoma which had been misdiagnosed as ABC. We herewith document a case of a pelvic ABC metastatic to the lung, liver, and kidneys. Diagnosis was confirmed by the presence of a break in the USP6 gene, which is pathognomonic for ABC, in a pulmonary metastasis of our patient. Sarcomatous transformation as an explanation for this behavior was ruled out by demonstrating diploid DNA content in both the pulmonary lesion and the primary tumor.

Cemented polyethylene cups in patients younger than 40 years.

UNLABELLED: Although uncemented cup implants frequently are used in young patients, we believe long-term survival rates of cups in these patients are somewhat disappointing, and therefore we have continued to use cemented cups in primary THA, even in young patients. However, in cases of acetabular bone stock defects, we also use bone impaction grafting. We prospectively followed 130 patients with 175 cemented cups; no patients were lost to followup. The mean age of the patients at surgery was 31 years (range, 16-39 years). An acetabular reconstruction with bone impaction grafting was performed in 84 hips (48%). The minimum followup was 2 years (average, 8.1 years; range, 2.0-18.5 years). Twenty-one of the 175 cups (12%) were revised at an average of 8.1 years (range, 2.0-18.5 years). Reasons for revision were infection (one early, seven late), recurrent dislocations (two), traumatic loosening (one), and aseptic loosening (10). The 10-year survival rate of all cemented cups with end point of revision for any cause was 85%. Survival with end point of aseptic loosening of all cups was 92%. Survival with end point of revision for aseptic loosening was 90% for the cups without impaction grafting and 95% for the cups with impaction grafting. We believe cemented acetabular cups in young patients have acceptable midterm survival; however, in the case of acetabular bone defects, we recommend reconstruction with impaction grafting. LEVEL OF EVIDENCE: Level III, therapeutic study.

Acetabular revision with impacted morselized cancellous bone graft and a cemented cup in patients with rheumatoid arthritis. A concise follow-up, at eight to nineteen years, of a previous report.

We previously reported our results at a minimum of three years after thirty-five revisions of total hip arthroplasty acetabular components in twenty-eight patients with rheumatoid arthritis. The revisions were performed with use of impacted morselized bone graft and a cemented cup. This update report presents the results at eight to nineteen years after the surgery, which, to our knowledge, is the longest follow-up available in the literature. No patient was lost to follow-up. Since our previous report, there were two additional cup failures due to aseptic loosening, at ten and sixteen years postoperatively. Kaplan-Meier analysis showed the probability of survival of the acetabular component at twelve years to be 80% (95% confidence interval, 65% to 95%) with removal of the cup for any reason as the end point and 85% (95% confidence interval, 71% to 99%) with aseptic loosening as the end point. Cup revisions performed with cement and use of impaction bone-grafting in patients with rheumatoid arthritis led to acceptable long-term prosthetic survival rates. This technique is attractive from a biological standpoint because of the possibility of maintaining acetabular bone stock.

The stability of impacted morsellized bone grafts in a metal cage under dynamic loaded conditions: an in vitro reconstruction of a segmental diaphyseal bone defect.

INTRODUCTION: Reconstructions of segmental diaphyseal bone defects with massive allografts are related to complications like nonunion and fractures. A reconstruction of these defects with a cage filled with an impacted morsellized bone graft could be an alternative. The bone graft in these cages should ideally be loaded to prevent resorption. Loading of morsellized bone grafts however can cause instability. The goal of this study was to assess the stability of an impacted morsellized bone graft in a cage under dynamic loaded conditions in an in vitro reconstruction of a segmental diaphyseal bone defect. The second goal was to assess the influence of cage type, washing of the graft and bone-cage fit. MATERIALS AND METHODS: Two different cage types were filled with impacted morsellized bone graft. The grafts were used washed and unwashed and in variable bone-cage fit conditions. We recorded the bone graft deformation in the cage under dynamic loaded conditions. RESULTS: Stability appeared to be not very sensitive to the cage type and whether the bone chips were washed or not. However, quality of the fit of the cage with the bone segment was an important parameter and should be optimized during surgery. CONCLUSIONS: Morsellized impacted bone graft in a cage is stable in dynamic loaded conditions in an in vitro reconstruction of a segmental diaphyseal bone defect. We believe that this method of reconstruction is a promising alternative for the reconstruction of large diaphyseal bone defects and should be tested relative to its biological merits in animal experiments.

Effect on tissue differentiation and articular cartilage degradation of a polymer meniscus implant: A 2-year follow-up study in dogs.

BACKGROUND: Replacement of the meniscus by an implant could potentially avoid cartilage degeneration. HYPOTHESIS: An implant of degradable polycaprolacton-polyurethane should act as a temporary scaffold enabling regeneration of a new meniscus by slow degradation of the polymer and simultaneous in-growth and differentiation of tissues into the typical cartilage-like tissue of the meniscus. STUDY DESIGN: Controlled laboratory study. METHODS: In 13 dogs' knees, the lateral meniscus was replaced with a porous polymer implant (6 and 7 for 6- and 24-month follow-up, respectively); in 7 knees only a meniscectomy was performed. In 6 knees, no surgery was performed. After 6 and 24 months, the implants and the articular cartilage were histologically evaluated. Compression-stress tests were performed on implant biopsy specimens. RESULTS: The implants were fully integrated into the tissue without formation of a capsule. The foreign body reaction did not exceed grade I. Differentiation from fibrous- to cartilage-like tissue was pronounced after 24 months. Viable cells were particularly absent after 24 months in central parts of the most anterior part of the scaffold. The mechanical properties of the implants were intermediate between the scaffold before implantation and native meniscus tissue and were not different between 6 and 24 months. After both 6 and 24 months, small areas of the implant were not covered with tissue. Cartilage degeneration was not prevented. CONCLUSION: A final remodeling of tissue into neomeniscus tissue could not take place since the original structure of the polymer was still present after 24 months. The implant did not prevent cartilage degradation. Several factors are discussed that may be responsible for this. CLINICAL RELEVANCE: Although clinical application of a polymer implant for the replacement of the entire meniscus is not supported by this study, the authors strongly believe in the concept, but further improvements in the implant and surgical technique are needed before such an implant can be recommended for human clinical use.

The cryosurgical treatment of chondroblastoma of bone: long-term oncologic and functional results.

BACKGROUND: Chondroblastoma of bone is a rare tumor that occurs most often in the epiphysis or apophysis of long bones. This benign tumor sometimes shows aggressive or malignant behaviour, and rarely metastases occur. Since wide resection often leads to growth impairment, intra-lesional curettage followed by an adjuvant therapy is developed to decrease the negative effects on growth and function without increased recurrence rates. PATIENTS AND METHODS: Between 1980 and 2001, 18 patients were treated for chondroblastoma of bone. Since 1989 cryosurgery has been used as an adjuvant treatment. The functional and oncologic results at follow-up were studied. RESULTS: Four patients were treated with curettage, and four with wide resection without adjuvant therapy. One patient developed a local recurrence and distant metastases. Ten patients were treated with curettage and cryosurgery. One patient developed a local recurrence 6 years later that was treated with curettage and cryosurgery again. No serious complications from cryosurgery occurred and the functional results at follow-up were excellent [mean MSTS score at follow-up 29]. CONCLUSIONS: Chondroblastoma of bone is a benign tumor with a relatively high recurrence rate. The local recurrence rates can be decreased with cryosurgery as a local adjuvant therapy with excellent functional results.

Epithelioid sarcoma: Still an only surgically curable disease.

BACKGROUND: Epithelioid sarcoma is a rare soft tissue sarcoma with a known high propensity for locoregional recurrence and distant metastases. The clinical behavior and prognostic factors that influence the survival of patients with epithelioid sarcoma were studied. METHODS: Twenty-three patients, including 16 men (70%) and 7 women (30%), who were treated for epithelioid sarcoma between 1979-2003 at the University Medical Center Groningen and Radboud University Nijmegen Medical Center, were reviewed retrospectively. The median age at diagnosis was 22 years (range, 1-54 years). At the time of diagnosis, 11 patients (48%) had metastases. Six patients with distant metastasis and 1 patient with an unresectable tumor received palliative treatment (30%). The remaining 16 patients underwent surgical treatment of local disease (11 patients) or locoregional disease (5 patients). Five patients in that group received isolated limb perfusion with tumor necrosis factor and melphalan. RESULTS: The 5-year and 10-year disease-free survival rates for all patients were 34% and 17%, respectively; for the 16 patients who received curative treatment, both rates were 56%. In the latter group, 8 patients developed local recurrence (50%) after a median follow-up of 4 months (range, 1-14 months). Nine patients were disease free after a median follow-up of 50 months (range, 6-290 months). Tumor size >5 cm (P < .0026) at diagnosis and local recurrence (P < .0008) were significant predictors of survival. CONCLUSIONS: The prognosis for patients with epithelioid sarcoma is poor, because a substantial number of patients present with extensive disease, lymph node metastases, and/or distant metastases. Treatment consists of radical surgical excision of the tumor and, if indicated, therapeutic lymph node dissection. In patients who have large tumors, isolated limb perfusion may be useful.

Replacement of the knee meniscus by a porous polymer implant: a study in dogs.

BACKGROUND: Meniscectomy will lead to articular cartilage degeneration in the long term. Therefore, the authors developed an implant to replace the native meniscus. HYPOTHESIS: The porous polymer meniscus implant develops into a neomeniscus and protects the cartilage from degeneration. STUDY DESIGN: Controlled laboratory study. METHODS: In a dog model, a porous polymer scaffold with optimal properties for tissue infiltration and regeneration of a neomeniscus was implanted and compared with total meniscectomy. The tissue infiltration and redifferentiation in the scaffold, the stiffness of the scaffold, and the articular cartilage degeneration were evaluated. RESULTS: Three months after implantation, the implant was completely filled with fibrovascular tissue. After 6 months, the central areas of the implant contained cartilage-like tissue with abundant collagen type II and proteoglycans in their matrix. The foreign-body reaction remained limited to a few giant cells in the implant. The compression modulus of the implant-tissue construct still differed significantly from that of the native meniscus, even at 6 months. Cartilage degeneration was observed both in the meniscectomy group and in the implant group. CONCLUSION: The improved properties of these polymer implants resulted in a faster tissue infiltration and in phenotypical differentiation into tissue resembling that of the native meniscus. However, the material characteristics of the implant need to be improved to prevent degeneration of the articular cartilage. CLINICAL RELEVANCE: The porous polymer implant developed into a polymer-tissue construct that resembled the native meniscus, and with improved gliding characteristics, this prosthesis might be a promising implant for the replacement of the meniscus.

Assessment of tissue ingrowth rates in polyurethane scaffolds for tissue engineering.

The continuous development of new biomaterials for tissue engineering and the enhancement of tissue ingrowth into existing scaffolds, using growth factors, create the necessity for developing adequate tools to assess tissue ingrowth rates into porous biomaterials. Current histomorphometric techniques evaluating rates of tissue ingrowth tend either to measure the overall tissue content in an entire sample or to depend on the user to indicate a front of tissue ingrowth. Neither method is particularly suitable for the assessment of tissue ingrowth rates, as these methods either lack the sensitivity required or are problematic when there is a tissue ingrowth gradient rather than an obvious tissue ingrowth front. This study describes a histomorphometric method that requires little observer input, is sensitive, and renders detailed information for the assessment of tissue ingrowth rates into porous biomaterials. This is achieved by examining a number of computer-defined concentric zones, which are based on the distance of a pixel from the scaffold edge. Each zone is automatically analyzed for tissue content, eliminating the need for user definition of a tissue ingrowth front and thus reducing errors and observer dependence. Tissue ingrowth rates in two biodegradable polyurethane scaffolds (Estane and polycaprolactone-polyurethane [PCLPU]) specifically designed for tissue engineering of the knee meniscus were assessed. Samples were subcutaneously implanted in rats with follow-up until 6 months. Especially at the earlier follow-up points, PCLPU scaffolds showed significantly higher tissue ingrowth rates than Estane scaffolds, making the PCLPU scaffold a promising candidate for further studies investigating meniscus tissue engineering.