Technical Factors

Despite clear benefits to health and mobility, the hesitancy to allow patients to return to sports remains strong. To what extent and just how safely patients can test the limits of their THR remains unclear. Studies demonstrate that many patients will return to a sport even against the doctor's recommendation [11]. The concern is multifactorial, and based in a desire to minimize a patient's risk and potential complications. Four main risks of sports participation after THR are dislocation, bearing wear, aseptic loosening, and periprosthetic fracture.

Instability

Postoperative hip dislocation is directly related to soft tissue integrity, approach, component position, and implant choice. The need to achieve a stable, impingement-free range of motion is even more crucial in the potential athlete. Maintenance of the soft tissue envelope decreases the risk of dislocation. Preserving the integrity of the posterior soft tissue provides the most stability, and is achieved either by maintaining tendinous attachments through an anterior or lateral approach [12], or by repairing capsular tissues and the short external rotators [13].

Intraoperatively, surgeons should ensure that hip does not demonstrate prosthetic or bony impingement. Prosthetic impingement in athletes can be minimized with larger head sizes, and even eliminated with head sizes greater than 36 mm [14]. Larger head sizes also increase the "drop distance" before potential dislocation, and the use of modified neck tapers maximizes head-to-neck ratios. Bony impingement is minimized with restoration of leg length and offset and the debridement of osteophytes. Optimal component position in the position of safety may also be enhanced with image guidance or computer navigation [15].

Wear

Bearing wear leads to osteolysis, aseptic loosening, and potential catastrophic failure, and the active athletic patient is at the greatest risk. Further, in the Swedish Registry a subgroup of active patients who were young heavy males had the highest historic incidence of THR failure [16]. Many of these concerns, however, arose because of the limitations of previously available bearing surfaces. Elevated levels of wear beyond 0.2 mm per year were a recognized problem with standard metal on polyethylene [17]. Enhanced alternative bearing

Fig. 3. Aseptic loosening of a cemented acetabulum developed 8 years after heavy athletic use in a 59-year-old professional tennis instructor.

surfaces promise a potential solution to activity-related wear. Although only long-term analysis will validate these claims, early-to-intermediate reports of ceramic on ceramic, metal on metal, and highly crosslinked polyethylene all show a significant reduction in annual wear rates [17,18]. With such a reduction in bearing wear, even the athletic patient is less likely to wear out the joint.

Aseptic Loosening

In addition to wear-induced loosening, higher loads from participation in sports stress the implant fixation surface. Early reports of failure in active patients were seen in cemented arthroplasties [1]. High repetitive loads led to fatigue fractures of the cement mantle, with eventual crack propagation (Fig. 3). Currently, cementless devices are more often chosen for this population, and may reduce the risk of fixation loss over time. Longer follow-up is necessary.

Periprosthetic Fracture

Aside from contact sports, most athletes are not at high risk of a periprosthetic fracture. Analysis of fracture risk describes more often a very different population than the motivated athlete [19]. Although possible, these fractures occur more commonly after a simple fall in the elderly patient who has poor balance and weakened bone.

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