Key Predictors for Returning to Running After Total Knee Arthroplasty: A Multifactorial Analysis

IQR is Inter Quartile Range, Sig. is P-Value

Table 6: Association of Running on TKR with Quantitative Factors.          

Discussion

This multi-factorial investigation was designed to identify potential correlating factors for returning to running after total knee arthroplasty, acknowledging its exploratory nature; our comprehensive statistical approach examined relationships across multiple variables where these findings represent correlations. While our study identifies predictive factors, future research is needed to establish specific pre-surgery running parameters and to evaluate the effectiveness of various post-operative rehabilitation protocols on running outcomes. After isolating key predictors, we plan to perform further studies to test for causality, explore mediating variables, and develop targeted interventions. Our results provide valuable insights that align with existing theoretical frameworks, offer meaningful direction for future research, and challenge current guidelines with the support of patients who wish to return to running following knee replacement surgery.

The online survey of members from the "TKR Runners" Facebook group found that a significant majority (79.2%) of respondents reported the ability to run following their knee replacement procedure. This finding challenges the cautionary guidance against high-impact activities like running after TKA, which has been previously advised by authors such as Kuster⁶ and supported by more recent studies [7,8].

Several factors showed significant associations with the likelihood of running post-operatively. Notably, those who stopped running for a shorter duration (1-2 years) prior to their TKA were more likely to achieve running post-surgery (p=0.041). Additionally, the median post-TKA duration was higher among runners (1.50 years) than non-runners (0.46 years) (p<0.001), suggesting that allowing adequate healing time influences outcomes. Current weekly running mileage also significantly influenced post-TKA running likelihood (p=0.044), with those running 35-40 miles per week being more likely to run post-TKA.

Interestingly, factors like prosthesis type/brand, use of cement, gender, complications, and formal physical therapy duration did not demonstrate significant impacts on the ability to run after TKA. This implies that barriers to resuming running after TKA may be more related to modifiable behavioral and lifestyle elements as opposed to fixed surgical variables. These findings align with the study by Antonelli et al. [8], which found that preoperative runners who returned to running had the highest Commitment to Exercise (CTE) scores and Brief Resilience Scale (BRS) scores, indicating exercise dependency and resilience. It is also worth noting that the TKA implants from the listed manufacturers (Zimmer Biomet, Stryker, Smith & Nephew, DePuy Synthes, and Confor MIS) share many similarities in their material composition. All five companies use cobalt-chromium alloy (Co-Cr-Mo) for the femoral component, which provides excellent wear resistance and biocompatibility [9,13].  Similarly, they all utilize titanium alloy (Ti-6Al-4V) with a porous coating for the tibial component, promoting bone ingrowth and long-term fixation [9,13].

However, there are some differences in the materials used for the tibial insert and optional patellar component. Zimmer Biomet and ConforMIS use ultra-high molecular weight polyethylene (UHMWPE) [9,13] while Stryker, Smith & Nephew, and DePuy Synthes employ highly crosslinked ultra-high molecular weight polyethylene (XLPE) [10,12]. XLPE has been introduced to improve wear resistance and reduce the risk of osteolysis compared to conventional UHMWPE [14]. Smith & Nephew stands out by offering an additional material option for the femoral component: oxidized zirconium (Oxinium) [11]. This material combines the strength of metal with the wear resistance and biocompatibility of ceramics, reducing the risk of polyethylene wear and subsequently osteolysis and aseptic loosening [15]. Overall, while there are minor variations in the materials used, particularly for the tibial insert and patellar component, the fundamental composition of the TKA implants remains similar across the mentioned manufacturers [9,13].

Recent machine learning analyses have provided new insights into preoperative functional predictors of successful return to running. Brennan-Olsen et al found that preoperative single-leg hop distance, quadriceps strength above 85% of the contralateral limb, and pre-surgery running volume were the strongest predictors of successful return to running post-TKA. These findings align with our results showing the significance of pre-TKA running patterns. Additionally, Tanaka et al's biomechanical analysis established specific progression criteria for return to running, emphasizing the importance of normalized gait patterns and adequate shock absorption during single-leg landing tasks before initiating impact activities. Their proposed three-phase return-to-running protocol, with specific biomechanical benchmarks required for progression between phases, offers a structured approach that could help explain why participants in our study who maintained longer running durations post-TKA showed better outcomes [13].

Furthermore, contemporary research by Nguyen et al examining long-term implant survival rates in running populations challenges traditional conservative approaches. Their findings showed that carefully progressed return to running did not significantly accelerate loosening or wear in patients using modern implant designs, with a reported 94% implant survival rate at 10 years in runners - comparable to non-running TKA patients [12]. This data supports our findings that prosthetic type and materials may be less crucial than previously thought, with behavioral and progression-based factors playing a more significant role in a successful return to running. Participation in organized running events was also significantly associated with the ability to run on the TKA with little to no pain (p<0.001). Runners who completed longer events such as 10k (p=0.049) and half marathon (p=0.044) were more likely to run on their TKA.

Moreover, individuals who reported running in organized events displayed a higher likelihood of achieving a full recovery (p<0.001). Conversely, those who had not fully recovered were more likely to report pre-existing health conditions such as depression (p<0.001) and a belief that they could not run again (p<0.001), highlighting the complex interplay between physical and mental aspects influencing running behavior after TKA.

While this study is limited by its reliance on self-reported survey data in a self-selected online community sample, it provides initial evidence challenging outdated absolute restrictions on higher impact activities like running following knee replacement. The results suggest that running after TKA may be successful for many motivated individuals, provided certain precautionary conditions are met regarding pre-surgery running behaviors and post-operative recovery protocols, such as motor imagery interventions and individualized perioperative multimodal pain management protocols [14,15].

However, as emphasized by the inconsistent surgeon recommendations reported in this study and the study by Antonelli et al [8], there is a clear need for evidence-based guidelines to help patients set realistic expectations and make informed decisions about their post-operative activities. Further longitudinal research is still warranted, potentially on quantifiable metrics of aseptic loosening, and exercise recommendations should remain individualized.

The current study remains valuable in contributing to the ongoing dialogue between patients and practitioners regarding the potential for returning to running after knee replacement. By documenting the subjective experiences of a larger sample of runners than previously reported, this research aims to provide a more comprehensive understanding of the factors that may influence the success of post-TKA running. These findings can help inform preoperative and postoperative decision-making, allowing patients and practitioners to set realistic expectations and develop individualized recovery plans that take into account the unique characteristics and goals of each patient.

Several potential sources of bias, including selection bias due to the sampling method, self-reporting bias, recall bias, and social desirability bias exist. The cross-sectional design also presented a risk of survivor bias and the lack of objective clinical measures and the potential for confounding variables were acknowledged as possible sources of bias.

To increase the study’s rigor, several measures were implemented to minimize potential biases. Clear inclusion criteria focused on participants who had undergone total knee arthroplasty, and respondents who reported partial knee arthroplasty were excluded to maintain consistency. The standardized survey design captured a comprehensive range of relevant factors including psychological factors, reducing the likelihood of missing variables. Anonymous online data collection encouraged transparency in responses, and statistical tests were selected to objectively analyze associations. While the study acknowledges the potential for selection bias, given the sample drawn from an active online community of TKA runners, the insights gained provide valuable direction for understanding factors associated with returning to running post-TKA.

 This study does not use data such as patient reported outcomes that provide knee-specific data for comparison with other studies, this can be used in future studies for patients that run status post total knee arthroplasty. Future randomized control studies with larger, diverse samples may further validate these findings and support generalizability. Additionally, the inclusion of varied surgical techniques into future studies by comparing robotic-assisted techniques to manual techniques would be imperative for improved implantation accuracy and potentially demonstrate increase overall patient outcomes and activity status with runners [16,18].

Conclusion

In summary, this study contributes to the growing body of evidence exploring the potential for returning to high-impact activities like running after knee arthroplasty. While more research is needed to establish definitive guidelines, the findings help open constructive dialogue between patients and providers on goals for potentially returning to running after a knee replacement procedure, taking into account individual factors and appropriate precautionary measures. The study highlights the importance of considering modifiable behavioral and lifestyle elements, as well as the complex interplay between physical and mental aspects, when discussing post-knee arthroplasty running with patients.

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