Increasing age is the biggest risk factor for the development and progression of knee joint osteoarthritis (OA).1, 2, 3 Knee OA is often a cause for significant pain, functional limitations, and overall decreased quality of life (QoL).4

Physical activity – including exercise focussing on lower limb muscle strength and weight control – is the most effective non-medical treatment in lower limb OA.5 Despite the advantages of a higher level of activity, other factors such as trauma and increased and more frequent loading, are at play in the aging athlete population, increasing the risk for developing knee OA.6,7

When conservative management fails, surgical treatment in the form of arthroplasty is a reliable and successful treatment. Arthroplasty has proven to be a highly effective surgical intervention to alleviate pain and restore function in patients with end-stage knee OA.8

Mirroring the evolving landscape of healthcare and the growing emphasis on maintaining an active lifestyle, even in the aging population, patients’ expectations have changed drastically over the past decades.9,10

In the aging athlete population, knee OA potentially poses unique challenges. These athletes present with specific clinical characteristics such as higher activity levels, better muscle strength, and higher expectations for postoperative function and sports performance. The management of knee OA in this population requires a comprehensive approach, integrating evidence-based principles with individualised treatment strategies.

In the aging athlete, the goal of knee arthroplasty has shifted from a mere focus on pain relief and functional improvement to a nuanced consideration of how the procedure can facilitate a return to specific athletic activities. Surgical technique and implant selection should account for the specific demands placed on the knee joint during sports activities. Customized rehabilitation protocols, tailored to individual goals and activity levels, play a pivotal role in achieving optimal postoperative outcomes. However, the need for a strong emphasis on realistic expectations remains crucial.

Despite the good outcomes observed in literature, there are certain considerations and potential challenges associated with arthroplasty in the aging athlete. One concern is the risk of accelerated wear and premature failure of the prosthetic components due to higher activity levels.

Unicompartmental Knee Arthroplasty (UKA) and Total Knee Arthroplasty (TKA) have established themselves as highly successful procedures, each with its own set of advantages and considerations. Success, in the context of knee arthroplasty, is multifaceted, encompassing pain relief, functional improvement, and the ability to return to desired physical activities. This chapter delves into the nuanced decision-making process, exploring the delicate balance between preserving healthy tissue and opting for a more comprehensive joint replacement in an athlete population.

Unicompartmental knee arthroplasty (UKA) is specifically designed for the treatment of isolated end-stage osteoarthritis in either the medial, lateral, or patellofemoral compartment of the knee. UKA allows the unworn, remaining compartments of the knee to remain intact and spares structures like the cruciate ligament containing mechanoreceptors that play an important role in propriocepsis.11 Leaving more of the native anatomy intact leads to a more naturally feeling knee after knee replacement surgery.12

In cases of isolated medial or lateral compartment wear, unloading osteotomies are a valuable alternative to UKA. Osteotomies around the knee have added advantages over UKA but are also subject to their own limitations. They can be used in younger patients, even in cases with lower grades of OA and have the potential to postpone the need for arthroplasty for several years. Additionally, the knee joint itself remains untouched by the procedure, and the unloaded compartment is protected from further wear. A potentially pathological alignment can be corrected, yet this potentially renders future conversion to TKA potentially more challenging.13,14 Once the osteotomy has healed, there are no restrictions in term of activities or even high-impact loading.15, 16, 17, 18 However, the result in term of pain relief is not as predictable as compared to UKA or TKA.19,20 In case of more severe grades of OA, the survival of osteotomies drops significantly, and UKA proves to be a more reliable long-term solution in the treatment of unicompartmental OA.15,19,21

The correct indication – as for many other procedures – strongly dictates the success of UKA.22 The original patient selection criteria published by Kozinn and Scott in 1989, have been extended to the currently used criteria.23,24 Nevertheless, one of the most important indicators for a satisfactory result after UKA remains the presence of Kellgren-Lawrence grade IV wear in a single compartment on weight bearing or stress X-rays.25

Sports related trauma with injuries to the menisci leading to meniscal dysfunction in the most loaded compartment of the knee, can accelerate the progression to single compartment end-stage OA as described above.6

For every type of UKA, return to sport (RTS) activity has been extensively documented in literature over the past decade.26 Systematic reviews and meta-analyses agree on a high rate of RTS rate between 74% and 100% for UKA, yet with a tendency towards lower impact sports and RTS at a lower level than pre-disease.15,27, 28, 29, 30, 31, 32, 33

Solving the problem of the narrower indication of UKA or osteotomies, and boasting a stronger survival in the registries, total knee arthroplasty (TKA) continues to be the gold standard operative treatment of end-stage knee OA.34 TKA has been able to show good results both overall and in terms of RTS – even in younger patients.35, 36, 37 The patient's age still plays an important role in the survivorship, generally making arthroplasty more suited for older patients.20

Depending on the alignment strategy, surgical technique, and the implant design, TKA can help treat knee joint instability or limb malalignment. The results for these different strategies are well documented.38, 39, 40, 41 Implant design also determines the level of constraint. Registry data teaches us that as constraint goes up, the survival of the implant goes down.42 This earlier failure could be explained by the higher internal stress and strain on the components.43 Although the kinematics of the knee joint might be affected by the choice of implant and level of constraint, this seems not to be the case for functional outcomes and RTS.36,44,45

The reported rate of RTS after knee arthroplasty is between 34% and 100%, depending on the study.46 The most important factors determining a higher likelihood of RTS were a higher preoperative activity level, younger age, lower BMI, and male gender.47,48 Overall, younger patients were able to achieve higher RTS rates and higher level of sporting activities when returning to sport postoperatively.47,49 The results tend to differ depending on the type of sport; different studies have focussed on RTS after golf, running, tennis, downhill skiing, etc.47,50, 51, 52 Overall, there is a consensus in literature about the higher return to low-impact sports and more limited participation in high-impact sports post arthroplasty.29,46,47,50, 51, 52, 53, 54, 55, 56, 57

An important predictor of post-operative participation in sports is the preoperative level of activity – specifically in the year prior to the procedure.58

After TKA, patients reportedly experience an overall positive effect on their ability to participate in physical activity, including sports, and reported patient satisfaction is high.49,59