Joint contact characteristics in agility total ankle arthroplasty.

High component contact pressures in total joint prostheses can lead to particle wear debris and prosthesis loosening. The contact pressures in the Agility total ankle prosthesis have not been investigated. In the current study, a cadaveric model was used to evaluate contact characteristics (average contact area, contact pressure, and contact peak pressures) for the Agility total ankle system. Ten cadaveric specimens were implanted with the Agility total ankle and axially loaded to 700 N. The average contact pressure of the system was 5.6 MPa with mean peak pressures of 21.2 MPa. In a separate phase of the study, contact characteristics with applied loads for each of the six component sizes showed a significant effect of component size on contact characteristics. When physiologic ankle forces are considered for normal patient activity, peak pressures observed in the current study may exceed recommended contact pressures (10 MPa) and the compressive yield point (13-22 MPa) for polyethylene. A heavy patient with a small ankle would not be expected to have a good outcome based on the current contact pressures data, whereas a heavy patient with a larger ankle might be a better candidate for surgery.

Proprioception of the knee before and after anterior cruciate ligament reconstruction.

PURPOSE: The purpose of this study was to determine, first, if there is measurable deficit in proprioception in an anterior cruciate ligament (ACL)-deficient knee, either compared to the contralateral knee or external controls; second, if this deficit, if present, improves after ACL reconstruction; and third, if improvement occurs, what the time course of improvement is. TYPE OF STUDY: Prospective cohort study. METHODS: Patients undergoing ACL reconstruction at the University of Chicago, demonstrating a full and painless range of motion and no other knee ligament injury or history of previous knee surgery, were eligible. Twenty-six patients, with an average age of 25 years (range, 16 to 48) were enrolled. Average time from injury to reconstruction was 8 weeks. The patients' contralateral knee served as an internal control, and 26 age-matched and gender-matched healthy volunteers were enrolled as an external control group. ACL reconstructions were performed using a single-incision technique with either bone-patellar tendon-bone or quadrupled hamstring autograft. They were allowed immediate weightbearing as tolerated and participated in a standardized rehabilitation program, with the goal of returning to sport at approximately 6 months. Proprioception testing was carried out using an electrogoniometer, in a seated position. Joint position sense (JPS) and threshold to detection of passive motion (TDPM) were measured preoperatively and at 3 and 6 weeks and 3 and 6 months postoperatively. RESULTS: Mean KT-2000 values 6 months postoperatively were 1.38 mm (+/-2). Modified Lysholm score improved significantly (P <.01). Calculated r values were 0.65 for JPS and 0.96 for TDPM. No significant differences in postoperative proprioception were found between hamstring and patellar tendon grafts or among patients with meniscus injury, meniscus repair, or chondral injury. Preoperatively, the mean TDPM in both the injured and contralateral knees was significantly higher (worse) than in the external control knees (P =.008; P =.016). Evaluation of changes in proprioception from preoperative to 6 months postoperative showed significant improvement in both injured and contralateral knees (P =.04; P =.01). At 6-month follow-up, there was no significant difference from controls. CONCLUSIONS: TDPM was a more reliable method than JPS for testing proprioception before and after ACL reconstruction in this study. Bilateral deficits in knee joint proprioception (TDPM) were documented after unilateral ACL injury. Reconstruction of a mechanical restraint (ACL graft) was believed to have a significantly positive impact on early and progressive improvement in proprioception.

Arthroscopic arthrodesis of the ankle, subtalar, and first metatarsophalangeal joint.

Arthroscopy of the foot and ankle should become part of the armamentarium of the foot and ankle surgeon. An arthroscopic fusion procedure of the ankle, subtalar, or first MTP joint is a viable alternative in certain patients. Appropriately selected patients (i.e., those with minimal bony deformity and without significant bone defects or avascular bone) can expect fusion rates at least equivalent to the standard open procedure. The benefits are truly magnified when one considers that these procedure result in a shortened hospitalization time, less pain as a result of the minimal surgical dissection and soft tissue stripping, and faster rehabilitation times. As results in the literature become available, these procedures can be expected to become an acceptable means of achieving the desired treatment goals.

Absorbable implants in fracture management.

The use of absorbable implants has been studied extensively in the clinic and the laboratory. The limitations of absorbable implants are now well-known and include a finite life span and strength profile, the possible development of an inflammatory response, and their limitation to use in fractures that do not require traditional compression techniques. Advantages of these implants include the lack of necessity for removal at a later date, which has cost savings potential, their ease of use, and their strength, which may be sufficient for healing in certain situations. The most likely scenarios for the use of these implants in fracture management of the foot and ankle include syndesmotic disruptions, dislocations about the midfoot, and fractures of the medial malleolus.