Return to Sport After Hip and Knee Arthroplasty: Counseling the Patient on Resuming an Active Lifestyle

Abstract

Purposeof Review

The purpose of this review is to summarize the available literature on the epidemiology, biomechanics, clinical outcomes, and complications of return to sport after TJA, as well as provide guidelines for patients’ safe return to athletic activity.

Recent Findings

As volume and indications for total joint arthroplasty (TJA) expand, arthroplasty candidates today are demographically younger, more physically active, and have higher expectations for postoperative function. Many TJA patients wish to resume sports activity that may theoretically place their reconstruction under more biomechanical stress and risk for early wear or failure. Recommendations for postoperative patient activity following TJA have historically largely been surgeon-dependent and in the context of evolving prosthetic design and surgical techniques.

Summary

We endorse a three-tiered framework for return to sporting activities: (1) low-impact sports are generally recommended, (2) intermediate-impact sports are generally recommended with experience, and (3) high-impact sports are generally not recommended though activity-specific joint decisions between patient and surgeon can be made.

Introduction

Total joint arthroplasty (TJA) has been shown to provide long-term pain relief and restoration of function in the degenerative hip and knee, and is best indicated following the failure of preceding nonoperative treatment modalities [1]. Primary TJA is one of the highest volume procedures performed each year in the USA. Annually, there are over 600,000 total knee arthroplasties (TKAs) and over 350,000 total hip arthroplasties (THAs) implanted [2]. By the year 2030, the combined number of primary TKA and THA is projected to rise above 1.5 million per annum.

Today’s arthroplasty patients are becoming younger and more active, with higher expectations for postoperative function. Primary TJA rates have increased by over 45% in patients less than 45 years old over the past 15 years [2]. As the incidence of these procedures increases within the younger demographics, surgeons are more frequently asked about the appropriateness of returning to sports and physical activities following primary TJA. Sporting and athletic activity expose the prosthetic joint to repetitive loading, potentially of supraphysiological forces, while extending the joint’s range of motion beyond traditional safe zones [3•]. As such, implant longevity concerns heighten in younger, active patients, given that prosthetic wear is a product of both time in situ and a function of use, alongside the added potential risks of instability and periprosthetic fracture [4, 5].

Current return to sport guidelines post primary TJA, published through the Hip Society, the Knee Society, and the American Association of Hip and Knee Surgeons (AAHKS), have been formulated via survey data and expert opinions, advising surgeons to make judgements based on each individual patient’s prior sporting and athletic experience [5, 6••]. To date, evidence-based consensus guidelines on return to sport post primary TJA have not been compiled. Paucity within the orthopedic literature on this topic has inspired a recent interest in the epidemiology and prognosis of athletic activity in the setting of prosthetic joints. The purpose of this review is to summarize the available literature on the epidemiology, biomechanics, clinical outcomes, and complications of return to sport after TJA, as well as provide guidelines for patients’ safe return to athletic activity.

Modern-Day Arthroplasty

Hip Arthroplasty

Contemporary THA in the USA has gradually shifted towards cementless fixation of both femoral and acetabular components over the last several decades, though hybrid fixation with cemented femoral components may still be indicated in patients with osteoporotic or irradiated bone that compromises biologic fixation [7•]. Despite relative risks and benefits, no surgical approach, whether direct anterior, anterolateral, direct lateral, or posterior, has been shown to be definitively superior and all are actively used in practice [8]. Similarly, various articular surface bearings are utilized in modern practice, including ceramic-on-polyethylene (CoP), metal-on-polyethylene (MoP), and ceramic-on-ceramic (CoC). The advent of modern highly crosslinked polyethylene in the late 1990s has reduced wear rates by up to 40 × compared to conventional polyethylene and has significantly impacted THA survivorship [9]. While metal-on-metal (MoM) hip arthroplasty gained popularity in the early 2000s due to the potential for reduced wear and dislocation risk, adverse soft tissue reactions to metal debris and associated high revision rates have largely led to a cessation of MoM implants for THA and a significant decrease in the use of hip resurfacing arthroplasty [9]. Satisfaction following primary THA ranges from 89 to 97% in the literature [10].

Knee Arthroplasty

Overall satisfaction ranges from 71 to 89% following primary TKA and 80 to 92% following unicompartmental knee arthroplasty (UKA) [10]. The lower patient satisfaction rates following TKA compared to THA remains a point of active research. While cemented TKA remains the gold standard and most widespread, cementless fixation with porous coated, osteoconductive implants have recently gained popularity, particularly for young patients with adequate bone stock to support osteointegration. Theoretical advantages of osteointegration include the potential for less long-term failure of cement interfaces under cyclic shear forces. Short- and mid-term survivorship appears comparable to cemented TKA, though long-term differences have not yet been assessed [11•]. The incidence of UKA, typically indicated for patients with unicompartmental disease without significant mechanical deformity and ligamentous compromise, has increased in recent years across all age groups [12]. Robotic technology has also recently gained popularity for knee (and hip) arthroplasty and has been shown to reduce the incidence of radiographic outliers [13]. Though present clinical outcomes data appears to be comparable to conventional TKA/UKA, there is optimism that accurate component positioning and knee balance will improve longevity. Patient satisfaction rates following primary TKA range from 75 to 93% [10].

Survivorship Data

Common indications for revision arthroplasty include infection, loosening, pain, polyethylene wear, instability, and periprosthetic fracture [9]. While long-term survivorship for hip and knee arthroplasty has been historically difficult to study, the development of national joint registries has helped reduce the potential for publication and selection biases from traditional case series. Pooled registry data, which include larger patient numbers and potentially less bias, represent the best generalizable evidence currently available (Table 1). In their pooled meta-analysis of article reporting minimum 15-year follow-up, Evans et al. reported the survivorship for primary conventional THA was 89.4% at 15 years, 70.2% at 20 years, and 57.9% at 25 years [14]. Pooled survivorship for TKA was reported at 93.0% at 15 years, 90.1% at 20 years, and 82.3% at 25 years [15]. UKA survivorship in comparison was reported at 76.5% at 1 years, 71.6% at 20 years, and 69.9% at 25 years [15]. It is important to note to patients that as modern implants and techniques (e.g., highly crosslinked polyethylene, cementless stems, and CoP) have more recently emerged, long-term survivorships of modern-day TJA may actually exceed these estimates, particularly for THA.

Table 1.

Long-term survivorship data of primary TJA

	15 years	20 years	25 years
THA [1]	89.4%	70.2%	57.9%
TKA [15]	93.0%	90.1%	82.3%
UKA [15]	76.5%	71.6%	69.9%

Source: Evans JT et al. Lancet 2019 [1, 15]

Biomechanics and Wear Characteristics Review

High impact or frequent physical activity places THA and TKA protheses at risk of aseptic loosening, polyethylene wear, instability, periprosthetic fracture, and periprosthetic infection. Primary TJA fixation can be achieved by way of cemented or cementless techniques. Cemented arthroplasty is advantageous in that polymethylmethacrylate (PMMA) cement acts as an elastic decoupling agent, interlocking with the trabeculae of cancellous bone. While curing, the viscoelastic properties of PMMA resist compression and convert axial load into hoop stresses that augment femoral fixation, acting to minimize acute subsidence thereafter [7•]. Cementless arthroplasty relies on acquiring initial mechanical stability, which subsequently facilitates bone ongrowth or ingrowth, depending on surface properties and prosthetic design [7•, 11•]. In both instances, physical activity, particularly involving torsional or tensile stress, can compromise stability at the implant-cement, cement-bone, and implant-bone interfaces [11•, 16].

Wear, or the progressive loss of bearing substance secondary to a combination of mechanical and corrosive action, can take the form of adhesive, abrasive, or third body wear. Macroscopic wear can occur in the setting of TKA, via subsurface delamination, followed by crevice corrosion and fracture propagation, leading to catastrophic failure of the prosthesis. Microscopic volumetric and linear wear are features more commonly associated with hip arthroplasty. Volumetric wear above 140 mm³/year and linear wear above 0.1 mm/year can stimulate an abnormal histiocytic response, leading to osteoclastic resorption of bone, known as osteolysis [17]. The clinical significance of osteolysis can often be underestimated on plain film radiographs in scenarios where the implant has undergone aseptic loosening. There is emerging evidence that this histiocytic response to wear debris can promote the recruitment of distant macrophages and leukocytes via chemotaxis, containing incompletely digested intracellular pathogens, and thus predispose an otherwise aseptic implant to periprosthetic infection by way of a “trojan horse” mechanism [18].

Range of motion beyond the traditional safe zone can place primary THA and TKA implants at risk for instability or fracture. Increasing femoral head size, thus allowing for a more favorable head-neck ratio, confers added stability when concerns arise [19]. Dual mobility articulations provide an additional bearing surface, which has been shown to reduce dislocation rates, but introduce additional risks such as intraprosthetic dislocations and mechanically assisted crevice corrosion [20]. TKA dislocations arise in the setting of flexion–extension mismatch, soft tissue attenuation, ligamentous injury, polyethylene wear, or in association with a fracture. Periprosthetic hip fractures most commonly occur about the femur, with cemented stems presenting most commonly with an “axe splitting” comminuted pattern, as opposed to the superolateral-to-inferomedial “sickle-like” pattern associated with their cementless counterparts [21].

Evidence and Guidelines on Return to Sport

Mirroring evolution in arthroplasty practice, clinical data on return to sport, and physical activities following TJA has been accumulating for several decades. Though prospective primary evidence on return to activities following TJA does exist, data have been primarily retrospective in nature. Furthermore, literature on return to activities following TJA is primarily survey-based and subject to inherent limitations, including volunteer bias, non-response bias, and recall bias. Most importantly, there is great heterogeneity in published study designs and inclusion criteria that present many potential confounders, including definitional differences in sports, impact, and activity levels. Nevertheless, clear trends have emerged on participation rates and outcomes with which to effectively counsel prospective arthroplasty patients. Here, we summarize historical and modern data on return to sports following THA, TKA, and UKA, as well as data on correlation of activity levels to outcome and potential failure.

Rates of Participation in Sports/Physical Activities

In general, return to sports and physical activity is considered the norm following TJA, with activity levels maintained or increased based on patient reporting and outcome scores. In their landmark prospective survey of 2085 patients’ activity levels before and after primary TJA, Wylde et al. reported that 61% of patients were able to return to their preferred activity within 1 to 3 years; this is compared to a 35% participation rate at 3 years prior to surgery [22••]. However, 26% of patients in this series remained unable to return to sporting activities, most commonly citing pain in either the operative extremity or elsewhere. In their recent meta-analysis of 18 original studies on TKA and UKA, Witjes et al. reported that the overall rate of return to sporting activities ranged from 36 to 89% following TKA and from 75 to 100% following UKA [23]. Using the impact activity levels previously defined by Healy et al. [3•], Witjes and colleagues also noted a shift in activity profile following TKA and UKA towards low- (94%) and intermediate-impact (64%) sports as opposed to high-impact sports (43%). In another recently published systematic review, Sowers and colleagues reported a mean return to sport rate of 82% (range, 55–100%) following THA [5]. They too found that the majority of patients were able to return to low- and intermediate-impact activities postoperatively, with a lower rate of return to high-impact activities. On the other hand, Dahm et al. reported that 16% of patients in their series of 1630 primary TKA patients participated in either heavy manual labor or sports deemed “not recommended” in previously published Knee Society guidelines [4]. In their series of THA patients < 75 years of age, Bonnin et al. similarly reported that 20% of patients participated in strenuous activity [24].

Prior studies have reported that, in general, higher activity levels and participation rates may be expected following THA compared with TKA [25, 26]. In a survey of 2366 postoperative arthroplasty patients, Arshi et al. reported a 76% sports participation rate following THA compared to 72% following TKA and 61% for those who had undergone both THA and TKA [27••]. They also noted significantly higher self-reported activity exertion and satisfaction among THA patients as well. However, Williams et al. found that patients undergoing THA and TKA had comparable postoperative activity levels when adjusting for other pre-surgical variables [28•]. More consistent evidence shows that participation rates and activity levels are greater in patients undergoing UKA compared to TKA [26].

Predictors of Participation in Sports/Physical Activities

The combined literature has consistently found that patient-specific rather than surgical factors are the main predictors of participation in sports and physical activities in TJA. In their retrospective review of 736 patients undergoing primary hip and knee arthroplasty, Williams et al. found that preoperative UCLA activity scores, younger age, male sex, and lower BMI were all independent predictors of activity level and participation, while type of surgery, implant, and surgeon preferences were not [28•]. These findings are consistent with Arshi et al., who found younger age, lower BMI, TKA, fewer medical comorbidities, and various physical outcome scores and mental health scores to independent predictors of postoperative participation in sport and physical activity. Among THA patients, Bonnin and colleagues found no difference in sports participation rates among patients undergoing anterior or posterior approach [8]. In addition to preoperative activity level, participation also correlates with both postoperative functional outcome scores and functional outcome score improvements compared to preoperatively. Furthermore, psychosocial factors have also been correlated with sports participation following TJA. Bonnin et al. reported that sports participation following THA was very strongly correlated with patients’ self-reported motivation (r = 0.97, p < 0.001) and was the greatest predictor of postoperative activity levels in their series, even greater than self-reported pain and activity scores [24]. Harbourne et al. found that patients with worse preoperative pain expectations were less likely to return to desired activity level than patients undergoing UKA [29]. Physical activity participation is also correlated with increased satisfaction following TJA. Approximately 20% of patients undergoing UKA or TKA report dissatisfaction with their arthroplasty outcome and multiple studies have demonstrated that the majority of these patients are either unable or unwilling to participate in sports [10]. Appropriate counseling of patients with these factors may help set appropriate preoperative expectations for patients considering TJA.

Time to Return to Sports/Physical Activities

Magan and colleagues previously reported two separate meta-analyses on the mean time to return to sport following THA and TKA [25, 26]. Using pooled data, they reported that return to sport rates were 19%, 70%, and 84% at 3, 6, and 12 months following TKA, respectively, with an overall adjusted return proportion of 88% at 14 months [26]. Their pooled data reported earlier return to sport rates following THA. Pooled rates of return were 40%, 77%, and 94% at 3, 6, and 12 months following THA, respectively [25]. Following UKA, time to return to sport is quicker than TKA and more comparable to THA. In meta-analysis, Radhakrishnan et al. reported return to sport rates of 48% at 3 months and 77% at 6 months following UKA [30]. It is important to note that time to return to sport is both widely variable for each patient and sport-specific. Robinson et al. reported mean time to return to golf was 4.4 months following TJA [31]. Conversely, more physically intense or impact-heavy activities such as skiing may require greater time to return to sport at a comparable level of activity [32]. It is important to note the difference between the mean achieved return to sport times previously reported and patient recommendations. According to recent surveys of arthroplasty surgeons [33], many providers have no specific time restrictions on postoperative activity levels, suggesting that patients on an individual basis may be safely advised to ease back into activities sooner. However, a survey of AAHKS members suggests that 3–6 months is the timeframe most commonly recommended by surgeons (61%) in counseling patients’ return to sport [6••].

Limitations in Return to Sports/Physical Activities

Though return to sports and physical activities remains the norm for most patients, 10–30% do not participate in sports and physical activities to a satisfactory level [5, 23]. Furthermore, up to 60% of patients report limitations in the time or intensity with which they are able to participate. Jassim and colleagues reported that fear of stressing the prosthetic joint and surgeon instruction are the two most common reasons patients cite for non-participation in their preferred activities following TJA [34]. Wylde et al. reported that the five most commonly reported reasons for not returning to sports were pain, inability to do required movements, medical advice, fear of damaging the joint, and lack of confidence [22••]. While self-imposed restrictions are a commonly cited reason for non-participation in sport, surgeon guidance merits specific discussion. In a survey of members of AAHKS, Swanson et al. reported that surgeons were often variable in their recommendations for return to intermediate- to high-impact activities and were typically more restrictive in recommendations for TKA compared to THA [33]. Arshi et al. demonstrated that while the majority of restrictions are self-imposed, surgeon or therapist advised restrictions are the second most common source of activity restriction after TJA. They also noted that more experienced, high-volume surgeons were more liberal in their postoperative recommendations. In their survey of 300 members of the German Arthroplasty Society, Vu-Han et al. reported that surgeons found risks associated with sports after THAs were minimal, with periprosthetic fracture, hip dislocation, and polyethylene wear being considered the highest risks [19]. Surgeons rated periprosthetic fracture, dislocation, and polyethylene wear as the highest estimated risks associated with sports after THA, with 77% of surgeons estimating the prevalence of sports-related revision surgery to be less than or approximately 1%.

Correlation of Activity Level with Failure in TJA

Though theoretical concerns for implant failure exist (e.g., periprosthetic fracture, dislocation, polyethylene wear, and aseptic loosening), evidence to associate failure with increased physical activity following TJA is limited. Early studies in the 1990s reported that increased activity level may be correlated with revision rates following THA. Kilgus et al. reported a twofold increased risk of aseptic loosening of cemented stems among patients regularly participating in sports and/or heavy labor activities. They reported that failures peaked in the 6–10-year postoperative period and was more common in patients with preoperative diagnoses other than osteoarthritis [16]. In another retrospective review of the Norwegian registry, Flugsrud et al. reported a higher rate of aseptic acetabular and femoral component loosening in men participating in intermediate or intensive recreational physical activity [35]. No association between physical activity and revision was noted in females in the cohort. Using an institutional registry of TKA patients 1008 patients matched 1:1, Ponzio and colleagues reported an increased rate of revision among physically active (3.2%) compared with inactive patients (1.6%) at 5–10 years postoperatively [36]. Instability and aseptic loosening were the most common indications for revision TKA.

On the other hand, most other modern studies, particularly since the advent of modern polyethylene bearing surfaces, have reported no difference between physical activity levels and failure at short- and mid-term follow-up [37–40]. In a retrospective series of 2532 patients who underwent THA with modern highly crosslinked polyethylene liners, Crawford et al. reported that all-cause and aseptic 5-year survivorship was equivalent between patients who had either high or low physical activity [40]. Mid-term data on modern UKA and TKA from their institution also showed no correlation between activity level and failure [38, 39]. Bearing surfaces, implant sizes, surgical approach, and fixation techniques may also influence surgeon recommendations, though direct evidence to support this has been limited. To the limited extent that they have been studied, modern bearing surfaces, surgical approach, and implant sizes have not been correlated with failure rates following TJA [8]. More dated studies correlating activity level and revision rates in THA have been more commonly described among cemented implants [16, 35]. Still, more long-term follow-up on modern arthroplasty techniques and bearings is warranted.

Sports-Specific Data

The four most common activities or sports in patients who underwent TJA are recreational walking, golf, cycling, and swimming [27••]. Golf has been the most extensively studied sport activity among TJA patients. Traditionally, the biomechanics of a golf swing has been divided into five phases (address, backswing, downswing, impact, and follow-through), which has differential trunk, hip, and knee muscle activity for the right and left lower body based on handedness [41]. Hip osteoarthritis can have decreased rotation and torque throughout each phase, while knee arthritis may cause difficulty in weight transfer from downswing through acceleration and follow-through. Fortunately, return to golf has been very favorable among TJA patients. In their meta-analysis of 23 studies, Robinson et al. reported an overall return to sport rate of 80% following TJA, with a higher rate of return to golf following THA (90%) compared to TKA (70%) at a mean of 4.4 months [31]. Evaluating game metrics, Mallon and Callaghan reported improvement in handicap ratings, driving distance, and functional outcome scores following TJA [42]. Papaliodis et al. reported at least twelve professional golfers who had undergone TJA with return to sport at the same level of competition [41].

Individual series of return to other sporting activities have also been published. Though skiing is often cautiously recommended by arthroplasty surgeons, Lancaster et al. reported a 70% rate of return to skiing, with no difference between patients undergoing hip or knee arthroplasty and no increased risk of revision at mean 4.4 years follow-up [32]. The majority of skiers had prior experience and were able to return to their prior level. In their series of 608 THA patients, Abe et al. reported that 3.8% of patients participated in recreational jogging postoperatively compared to 5.4% preoperatively [43]. At 5-year follow-up, there was no evidence of aseptic loosening, subsidence, increased serum metal ion levels, or excessive polyethylene wear noted among joggers, suggesting that this relatively high-impact sport may be well tolerated among well-suited patients. Mont and colleagues surveyed 33 competitive tennis players from the United States Tennis Association who had undergone TKA at a mean follow-up of 7 years [44••]. Players reported a significant mean improvement in overall mobility, ability to play on various surfaces, weight shifting, and follow-through. Two of the 46 TKA performed required revision for polyethylene wear at 8 and 11 years postoperatively and remained asymptomatic at 5 and 7 years after revision, respectively.

Guidelines and Recommendations

As there are no prospective randomized studies that delineate guidelines for safe and appropriate physical activities following TJA, current recommendations are largely based on the data summarized here and surgeons’ personal beliefs and experiences. In 1999, Healy et al. surveyed members of the Hip Society and used responses to describe a three-tiered framework for return to sporting activities: (1) low-impact sports are generally recommended, (2) intermediate-impact sports are generally recommended with experience, and (3) high-impact are generally not recommended [3•]. Since then, several minor updates and addendums have been made to this initial iteration based on surveys of members of AAHKS and the interpretation of new data and sports classification. The most recent versions of these recommendations, based on consensus statements from AAHKS, the Hip Society, and Knee Society, for both THA and TKA are summarized in Table 2 [6••, 45]. Furthermore, the largest group of surgeons recommend return to activities at 3 to 6 months postoperatively, with a minority allowing return within the first 3 months [6••]. Caution is provided that the risk of implant failure is theoretically proportional to the cumulative impact sustained by the prosthetic joint, such that predictions of risk of failure cannot be made for an individual patient. In addition to the sport-specific framework provided, these consensus statements emphasize the importance of common sense by both patients and surgeons in decision-making regarding activities, moderation of all activities, and the importance of general physical and athletic fitness prior to resuming specific physical activities (Table 3).

Table 2.

Activity recommendations following total joint arthroplasty based on AAHKS, Hip Society, and Knee Society consensus statements

Low-impact sports: recommended	Intermediate-impact sports: recommended with experience	High-impact sports: generally not recommended*
Golf	Doubles tennis	Running/jogging
Swimming	Stair climber	Basketball
Walking	Hiking	Soccer
Treadmill	Downhill skiing	Baseball/softball
Stationary bicycle	Snowboarding	Racquetball/squash
Elliptical machine	Weightlifting	Martial arts
Cycling	Ice skating/roller blading	Volleyball
Rowing	Aerobics	American Football
Dancing	Horseback riding	Rugby
Pilates		Singles tennis
Stationary skiing
Water aerobics
Bowling
Table tennis

Table 3.

Sport-specific rates of return to sport

	Return to sport	Citation
Golf	80%	[31]
Skiing	70%	[32]
Tennis	100%	[44••]
Jogging	3.8%	[43]

Conclusion

Evolution in the implants and techniques of modern day-arthroplasty has facilitated the return to sports/physical activities as the norm in the majority of TJA patients. Though patients may note a shift in the activities and sports in which they participate, the majority of patients are satisfied with their ability to participate in sports and modern evidence suggests that a judicious return to activities is safe. Current guidelines advise returning to sport activities based on their relative impact-level with low- and intermediate-impact generally recommended with experience. Patients should be appropriately counseled on these activity-specific postoperative expectations and outcomes and make a joint decision with their orthopedic surgeon.

Declarations

Conflict of Interest

Dr. Arshi has no conflicts of interest to declare. Dr. Hughes has no conflicts of interest to declare. Dr. Robin has no conflicts of interest to declare. Dr. Parvizi declares the following potential conflicts of interest: 3 M: research support; Acumed, LLC: stock or stock options; Aesculap: research support; Alphaeon: stock or stock options; AO Spine: research support; Becton Dickenson: IP royalties; paid consultant; Biomet: research support; Cardinal Health: paid consultant; Cempra: research support; CeramTec: research support; Ceribell: stock or stock options; Coracoid: stock or stock options; Corentec: IP royalties; paid consultant; Datatrace: publishing royalties, financial or material support; DePuy: research support; Elsevier: publishing royalties, financial or material support; Elute: stock or stock options; Ethicon: paid consultant; Hip Innovation Technology: stock or stock options; Illuminus: stock or stock options; Integra: research support; Intellijoint: stock or stock options; Jaypee Publishers: publishing royalties, financial or material support; KCI/3 M (Acelity): paid consultant; Lima: research support; MicroGenDx: paid consultant; Molecular Surface Technologies: stock or stock options; Myoscience: research support; Nanooxygenic: stock or stock options; National Institutes of Health (NIAMS & NICHD): research support; NDRI: research support; Novartis: research support; OREF: research support; Orthospace: research support; Osteal: stock or stock options; Parvizi Surgical Innovations and Subsidiaries: stock or stock options; Peptilogic: stock or stock options; Peptilogics: paid consultant; Pfizer: research support; PRN-Veterinary: stock or stock options; Rotation Medical: research support; Simplify Medical: research support; SLACK Incorporated: publishing royalties, financial or material support; Smith & Nephew: research support; Sonata: stock or stock options; Stelkast: research support; Stryker: research support; Synthes: research support; Tenor: paid consultant; TissueGene: research support; Tornier: research support; Wolters Kluwer Health-Lippincott Williams & Wilkins: publishing royalties, financial or material support; Zimmer Biomet: paid consultant; research support. Dr. Fillingham declares the following potential conflicts of interest: board or committee member; American Association of Hip and Knee Surgeons: board or committee member; Exactech, Inc: IP royalties; paid consultant; Johnson & Johnson: paid consultant; Medacta: IP royalties; paid consultant; MicroGen Dx: other financial or material support; Parvizi Surgical Innovations: stock or stock options; Saunders/Mosby-Elsevier: publishing royalties, financial or material support; Zimmer: paid consultant.

Human and Animal Rights and Informed Consent

This article does not contain any studies with human participants or animals performed by any of the authors.