Foot Strike Run Retraining for Patients With Patellofemoral Chondral Defects: A Case Series.

Military service members (SMs) demonstrate high rates of patellofemoral chondral defects (PFCDs) that are difficult to diagnosis and, if untreated, result in a cascade of events eventually leading to osteoarthritis. Running is an essential occupational task for SMs; however, there is little evidence regarding techniques to maintain running ability in individuals with cartilage defects. The purpose of this case series was to assess the clinical application of foot strike run retraining in patients with PFCDs. This case series included two active duty U.S. Marine Corps SMs who presented to outpatient physical therapy with PFCD, diagnosed via MRI. Both patients attended eight foot strike run retraining sessions. Running mechanics and patient-reported outcomes were recorded pre-training, post-training, and at a 1-month follow-up visit. Both patients successfully converted their strike pattern from a rearfoot to a non-rearfoot strike pattern with training and retained this strategy at 1-month follow-up. Post-intervention, both patients demonstrated increased running tolerance, and improvements in Numeric Pain Rating Scale and Lower Extremity Functional Scale scores. Biomechanical analysis showed that both patients demonstrated a 63% to 70% reduction in average and peak vertical ground reaction force loading rates post-treatment. Modification of foot strike pattern from rear to non-rearfoot strike during running for individuals with PFCD can reduce the magnitude of impact loading, which potentially limits disease progression. These findings suggest that foot strike run retraining may be a feasible strategy to reduce pain and improve function in SMs with PFCD who are required to run for occupational responsibilities.

Patient-specific implants with custom cutting blocks better approximate natural knee kinematics than standard TKA without custom cutting blocks.

BACKGROUND: Nearly 14% to 39% TKA patients report dissatisfaction causing incomplete return of function. We proposed that the kinematics of knees implanted with patient-specific prostheses using patient-specific cutting guides would be closer to normal. METHODS: Eighteen matched cadaver lower limbs were randomly assigned to two groups: group A was implanted with patient-specific implants using patient-specific cutting guides; group B, the contralateral knee, was implanted with a standard design using intramedullary alignment cutting guides. Knee kinematics were measured on a dynamic closed-kinetic-chain Oxford knee rig, simulating a deep knee bend and in a passive rig testing varus-valgus laxity. RESULTS: The difference from normal kinematics was lower for group A compared to group B for active femoral rollback, active tibiofemoral adduction, and for passive varus-valgus laxity. CONCLUSIONS: Our results support the hypothesis that knees with patient-specific implants generate kinematics more closely resembling normal knee kinematics than standard knee designs. CLINICAL RELEVANCE: Restoring normal kinematics may improve function and patient satisfaction after total knee arthroplasty.

Effect of head diameter on passive and active dynamic hip dislocation.

Hip dislocation is a major short-term complication after total hip arthroplasty (THA). One factor thought to reduce the risk for dislocation is head size. We constructed subject-specific computer models to study the effect of head size on risk for postoperative dislocation. Femoral and acetabular geometry was constructed after segmenting CT scans of nine hips. CAD models of THA components with four head diameters (28, 32, 36, and 44 mm) were virtually implanted. Hip capsular ligaments were simulated using rigid-body ellipsoids connected by non-linear springs. Posterior dislocation was simulated during a rise from a low chair; anterior dislocation was simulated during a pivot activity. Intraoperative stability tests were simulated for anterior or posterior dislocation. While rising from a low chair (posterior dislocation) and during the pivot activity (anterior dislocation), increasing head size significantly increased hip flexion angle at dislocation and generated higher dislocation moments. Larger heads reduced the risk for dislocation. Intraoperative stability tests detected the relative increased resistance to dislocation despite differences in the absolute magnitude of moments. This model can be useful preclinical tool for assessing design changes, the effect of component placement, and the activity-based risk for dislocation.

Bony impingement limits design-related increases in hip range of motion.

BACKGROUND: Factors affecting risk for impingement and dislocation can be related to the patient, implant design, or surgeon. While these have been studied independently, the impact of each factor relative to the others is not known. QUESTIONS/PURPOSES: We determined the effect of three implant design factors, prosthetic placement, and patient anatomy on subject-specific ROM. METHODS: We virtually implanted hip geometry obtained from 16 CT scans using computer models of hip components with differences in head size, neck diameter, and neck-shaft angle. A contact detection model computed ROM before prosthetic or bony impingement. We correlated anatomic measurements from pelvic radiographs with ROM. RESULTS: When we implanted the components for best fit to the subject's anatomy or in the recommended orientation of 45° abduction and 20° anteversion, ROM was greater than 110° of flexion, 30° of extension, 45° of adduction-abduction, and 40° of external rotation. Changes in head size, neck diameter, and neck-shaft angle generated small gains (3.6°-6°) in ROM when analyzed individually, but collectively, we noted a more substantial increase (10°-17°). Radiographic measurements correlated only moderately with hip flexion and abduction. CONCLUSIONS: It is feasible to tailor implant placement to each patient to maximize bony coverage without compromising ROM. Once bony impingement becomes the restricting factor, further changes in implant design may not improve ROM. Radiographic measurements do not appear to have value in predicting ROM.