Validation of a 3D CT method for measurement of linear wear of acetabular cups: A hip simulator study

Background We evaluated the accuracy and repeatability of a 3D method for polyethylene acetabular cup wear measurements using computed tomography (CT). We propose that the method be used for clinical in vivo assessment of wear in acetabular cups. Material and methods Ultra-high molecular weight polyethylene cups with a titanium mesh molded on the outside were subjected to wear using a hip simulator. Before and after wear, they were (1) imaged with a CT scanner using a phantom model device, (2) measured using a coordinate measurement machine (CMM), and (3) weighed. CMM was used as the reference method for measurement of femoral head penetration into the cup and for comparison with CT, and gravimetric measurements were used as a reference for both CT and CMM. Femoral head penetration and wear vector angle were studied. The head diameters were also measured with both CMM and CT. The repeatability of the method proposed was evaluated with two repeated measurements using different positions of the phantom in the CT scanner. Results The accuracy of the 3D CT method for evaluation of linear wear was 0.51 mm and the repeatability was 0.39 mm. Repeatability for wear vector angle was 17?. Interpretation This study of metal-meshed hip-simulated acetabular cups shows that CT has the capacity for reliable measurement of linear wear of acetabular cups at a clinically relevant level of accuracy

Biomechanics of two types of bone-tendon-bone graft for ACL reconstruction.

We measured the initial fixation strength of a new graft, bone-hamstring-bone (BHB), for reconstruction of the anterior cruciate ligament (ACL) in 79 porcine knees and compared it with that of the normal porcine ACL and of the bone-patellar tendon-bone (BPB) graft. All specimens were subjected to ultimate load to failure and cyclic loading tests to assess the amount of graft slippage. The ultimate load to failure for the intact ACL was 1266 +/- 250 N, for the BPB graft 663 +/- 192 N and for the BHB graft 354 +/- 92 N (p < 0.01). After cycling to 235 N (the maximum load for all groups without failure) the average residual displacements after removal of the load for the ACL, BPB and BHB grafts were 0.031 +/- 0.013 cm, 0.078 +/- 0.033 cm, and 0.322 +/- 0.222 cm, respectively (p < 0.01). For the BHB graft the load to failure was less and the amount of graft slippage was more than for the BPB graft. Neither form of reconstruction was as strong as the intact ACL

Hydroxyapatite-coated distal femoral replacements. Preliminary results.

A custom-designed, hydroxyapatite-coated distal femoral replacement was developed and implanted in five individuals at the authors' hospital. The indications for this type of prosthesis were a multiply failed cemented endoprosthesis in two individuals; a revision of an infected, previously cemented endoprosthesis in another; a primary low-grade sarcoma in a fourth, and a stage III giant cell tumor in the final individual. Mean follow-up time was 3.3 years (range, 2.9-3.5 years). The functional results, based on the Musculoskeletal Tumor Society (MSTS) criteria, were excellent in one patient (20%) and good in four patients (80%). Musculoskeletal Tumor Society functional scores ranged from 25 to 35 (mean, 29.8). No patient had thigh pain. All the femoral components appeared well fixed on radiographic evaluation. These preliminary results indicate that a hydroxyapatite-coated distal femoral replacement may represent a viable alternative to a cemented endoprosthesis for aggressive benign lesions and low-grade sarcomas requiring resection. In addition, it appears to be a viable solution for failed cemented endoprostheses in individuals who have survived their disease

Hydroxyapatite-coated distal femoral replacements. Preliminary results.

A custom-designed, hydroxyapatite-coated distal femoral replacement was developed and implanted in five individuals at the authors' hospital. The indications for this type of prosthesis were a multiply failed cemented endoprosthesis in two individuals; a revision of an infected, previously cemented endoprosthesis in another; a primary low-grade sarcoma in a fourth, and a stage III giant cell tumor in the final individual. Mean follow-up time was 3.3 years (range, 2.9-3.5 years). The functional results, based on the Musculoskeletal Tumor Society (MSTS) criteria, were excellent in one patient (20%) and good in four patients (80%). Musculoskeletal Tumor Society functional scores ranged from 25 to 35 (mean, 29.8). No patient had thigh pain. All the femoral components appeared well fixed on radiographic evaluation. These preliminary results indicate that a hydroxyapatite-coated distal femoral replacement may represent a viable alternative to a cemented endoprosthesis for aggressive benign lesions and low-grade sarcomas requiring resection. In addition, it appears to be a viable solution for failed cemented endoprostheses in individuals who have survived their disease

Evaluation of rhBMP-2 with an OPLA carrier in a canine posterolateral (transverse process) spinal fusion model.

Study designPosterolateral L4-L5 transverse process fusions were done on 14 adult beagles. Six were implanted with recombinant human bone morphogenetic protein-2 carried by open-cell polylactic acid polymer delivery vehicle. Six received autogenous iliac bone graft. Two received carrier alone. Eleven were killed 3 months after implantation. One in each group was maintained for 8 months.ObjectivesTo compare recombinant human bone morphogenetic protein-2 and open-cell polylactic acid polymer with autogenous iliac bone for inducing transverse process fusion in the canine by 3 months and to determine whether transverse process decortication and implantation of carrier alone causes spontaneous transverse process fusion in the canine.Summary of background dataRecombinant human bone morphogenetic proteins have healed segmental long bone defects in several models. They have induced interlaminar and facet fusions in canines. Interlaminar and facet fusions have occurred after sham decortications in canines. Recombinant human bone morphogenetic protein-2 has not been evaluated for transverse process fusion in canines. Transverse process fusion is a preferred clinical method for achieving posterior lumbar fusion.MethodsFusion sites were evaluated by serial computed tomography scans. After the dogs were killed, explanted spines were subjected to manual testing, mechanical testing, high resolution radiography, and histologic analysis.ResultsOne hundred percent of recombinant human bone morphogenetic protein-2-implanted sites had solid transverse process fusion by 3 months according to all measures. No autografted sites were fused at this interval. Osseous bridging of posterolateral gutters occurred in the recombinant human bone morphogenetic protein-2-implanted sites after 2 months, the earliest radiographic measure. None of the carrier-only sites showed bone formation.ConclusionsRecombinant bone morphogenetic protein-2 carried by open-cell polyactic acid polymer is superior to autogenous iliac bone for producing radiographically and mechanically solid transverse process fusions in canines by 3 months. Spontaneous transverse process fusion does not occur in canines after decortication and open-cell polylactic acid polymer implantation

Evaluation of rhBMP-2 with an OPLA carrier in a canine posterolateral (transverse process) spinal fusion model.

Study designPosterolateral L4-L5 transverse process fusions were done on 14 adult beagles. Six were implanted with recombinant human bone morphogenetic protein-2 carried by open-cell polylactic acid polymer delivery vehicle. Six received autogenous iliac bone graft. Two received carrier alone. Eleven were killed 3 months after implantation. One in each group was maintained for 8 months.ObjectivesTo compare recombinant human bone morphogenetic protein-2 and open-cell polylactic acid polymer with autogenous iliac bone for inducing transverse process fusion in the canine by 3 months and to determine whether transverse process decortication and implantation of carrier alone causes spontaneous transverse process fusion in the canine.Summary of background dataRecombinant human bone morphogenetic proteins have healed segmental long bone defects in several models. They have induced interlaminar and facet fusions in canines. Interlaminar and facet fusions have occurred after sham decortications in canines. Recombinant human bone morphogenetic protein-2 has not been evaluated for transverse process fusion in canines. Transverse process fusion is a preferred clinical method for achieving posterior lumbar fusion.MethodsFusion sites were evaluated by serial computed tomography scans. After the dogs were killed, explanted spines were subjected to manual testing, mechanical testing, high resolution radiography, and histologic analysis.ResultsOne hundred percent of recombinant human bone morphogenetic protein-2-implanted sites had solid transverse process fusion by 3 months according to all measures. No autografted sites were fused at this interval. Osseous bridging of posterolateral gutters occurred in the recombinant human bone morphogenetic protein-2-implanted sites after 2 months, the earliest radiographic measure. None of the carrier-only sites showed bone formation.ConclusionsRecombinant bone morphogenetic protein-2 carried by open-cell polyactic acid polymer is superior to autogenous iliac bone for producing radiographically and mechanically solid transverse process fusions in canines by 3 months. Spontaneous transverse process fusion does not occur in canines after decortication and open-cell polylactic acid polymer implantation