The Effect of Sensory Deficit After Total Knee Arthroplasty on Patient Satisfaction and Kneeling Ability.

BACKGROUND: Skin numbness after total knee arthroplasty is a common complication. The incidence in the literature is variable from 27% to 100%. However, there is conflicting evidence about the consequences of this complication. The purpose of this study was to evaluate if postoperative numbness influenced patient satisfaction or kneeling ability.
METHODS: We recruited patients who underwent a total knee arthroplasty for osteoarthritis one to 5 years before the study. Sensation was measured using a Semmes-Weinstein, 10-gram monofilament. Measurements were taken in several zones around the incision, and overall sensory status was classified as full numbness, partial numbness, and no numbness. Patients completed a questionnaire evaluating their subjective numbness, overall satisfaction, and kneeling ability. We evaluated the effect of numbness on satisfaction and function.
RESULTS: A total of 96 patients were enrolled. Thirty-four patients were classified as no sensory deficit, 29 as partial deficit, and 33 as full deficit. There were no differences in demographics. Out of all the patients that were found to have a sensory deficit, 54.8% of them did not report any subjective numbness. Average patient-reported satisfaction scores were 8.76/10, 8.97/10, and 8.48/10 for no numbness, partial numbness, and full numbness, respectively. Eleven out of 96 patients noted an inability to kneel. There was no statistical difference for satisfaction scores or kneeling ability between the groups.
CONCLUSION: Sensory deficit after total knee arthroplasty is a frequently reported complication. However, the majority of the patients do not report subjective sensory deficits. Postoperative numbness does not appear to affect patient satisfaction or kneeling ability.

Introduction

Numbness surrounding the incision after total knee arthroplasty is a frequently reported outcome with rates ranging from 27% to 100% [[1], [2], [3]]. Denervation is caused by damage to the medial femoral cutaneous nerve and infrapatellar branch of the saphenous nerve which course from medial to lateral and provide sensation to the lateral skin [4]. Both nerves are disrupted during routine total knee arthroplasty by traditional midline incisions [4]. There is conflicting evidence about the significance of postoperative skin numbness, and the overall effect on patient outcomes is largely unknown.

Several studies have failed to demonstrate reduced Patient-Reported Outcome Measures (PROMs) as a consequence of postoperative skin numbness [2,[5], [6], [7], [8]]. Jariwala et al. [5] reported a 53% incidence of skin numbness after total knee arthroplasty but failed to show any effect on Knee Society Scores.

Up to 20% of patients undergoing total knee arthroplasty are not satisfied after the surgery, and although the reasons are still unknown, postoperative numbness may be a contributing factor [[9], [10], [11]]. In particular, the inability to kneel after surgery as a result of sensory deficit has been hypothesized to account for patient dissatisfaction [[12], [13], [14], [15]].

The objective of this study was to identify the incidence and the characteristics of postoperative numbness. The secondary objective of the study was to evaluate if there was any correlation between postsurgical sensory disturbance and patients’ clinical outcomes including overall satisfaction and ability to kneel.

Material and methods

Data were collected prospectively after obtaining Health Science Research Ethics Board approval. Patients presenting for follow-up appointments were recruited consecutively. We recruited patients older than 18 years who underwent a total knee arthroplasty for osteoarthritis 1-5 years before the study start date. Exclusion criteria included patients with revision knee arthroplasties, additional surgeries or previous trauma to the knee of interest, history of infection, peripheral or central neurologic impairment, inflammatory articular disease, and the inability to speak or read English.

Eligible and consenting patients were asked to fill in a questionnaire about numbness and its effect on daily activities in addition to basic demographic information (Appendix A). Satisfaction was rated on a Likert scale from 1—completely dissatisfied—to 10—completely satisfied. Ability to kneel was rated as “No Affect”, “Minimal Affect”, “Some Affect”, and “Complete Affect” or “I cannot recall doing this activity”. Sensation was measured using a Semmes-Weinstein, 10-gram monofilament. The 10-gram monofilament has become a widely used test for neuropathy because of its accuracy, low cost, and convenience [16,17]. Three measurements were taken in 4 separate zones on the lateral aspect of the incision and recorded as sensation absent or present. The same measurements were carried out on the medial aspect of the incision to be used as control. Sensation status in each zone was classified based on the majority (2/3) of measurements. Overall sensory deficit was classified as follows: (1) no sensation in all 4 zones, full numbness; (2) sensation present in at least one zone but less than 4, partial numbness; and (3) sensation present in all 4 zones, no numbness.

Statistical analysis was performed with SPSS (IBM, Armonk, NY) version (25) using analysis of variance or the Kruskal-Wallis test for distribution violations to assess between group differences in continuous outcomes. Chi-square analysis or Fisher exact test was used to test for differences in categorical outcomes. A P value of less than .05 was considered statistically significant.

Results

A total of 96 patients were enrolled into the study. Thirty-four patients (36%) were classified as having no sensory deficit, 29 (30%) as partial deficit, and 33 (34%) as full deficit. A total of 9 patients had numbness on the medial side of the incision with 7 graded as partial and 2 severe. There were no differences in demographics based on sensory status (Table 1). A total of 28 patients (29.1%) reported having numbness around their incision with the subjective questionnaire; however, 62 patients (64.3%) had evidence of sensory impairment upon monofilament testing (Table 2). Interestingly, 20.6% of patients that did not have any evidence of sensory impairment with monofilament testing reported subjective numbness while 48.5% of patients that had complete loss of sensation did not report subjective numbness (Table 2).

Table 1

Patient demographics.

	Sensory status
	No numbness	Partial numbness	Full numbness	P value
Gender (% female)	61.8%	55.2%	48.5%	.55
Age (mean ± SD)	68.33 ± 6.02	69.39 ± 8.07	68.67 ± 11.37	.89
BMI (mean ± SD)	33.49 ± 7.32	34.19 ± 6.07	33.82 ± 6.45	.916
Follow-up (mean ± SD)	3.09 ± 1.40	3.11 ± 1.48	2.27 ± 1.44	.033
Incision length cm (mean ± SD)	19.35 ± 1.89	20.52 ± 2.09	20.67 ± 2.69	.037

Table 2

Patient reported numbness compared to measured monofilament testing.

	Sensory status
	No numbness	Partial numbness	Full numbness
Patient reported numbness
No	27 (79.4%)	18 (62.1%)	16 (48.5%)
Yes	7 (20.6%)	11 (37.9%)	17 (51.5%)
Total	34 (35.1%)	29 (30.2%)	33 (34.3%)

Average patient-reported satisfaction scores were 8.76 (1.69), 8.97 (1.18), and 8.48 (1.64) for no numbness, partial numbness, and full numbness groups, respectively (P = .466) (Fig. 1). When asked if patients were happy with their total knee replacement, 88.2% answered “yes” in the no numbness group, 100% in the partial numbness group, and 90.9% in the full numbness group.

Figure 1

Patient satisfaction based on objective testing.

A small portion of patients, 11 out of 96, noted an inability to kneel (Table 3). No difference was detected in the ability to kneel between postoperative numbness categories (P = .42).

Table 3

Affect of skin numbness on kneeling ability (P = .42).

	Kneeling ability
	No affect	Some or complete affect	Cannot recall
No numbness
Patients	7	2	25
%	20.6%	5.9%	73.5%
Partial numbness
Patients	5	6	18
%	17.2%	20.7%	62.1%
Full numbness
Patients	9	3	21
%	27.3%	9.1%	63.6%

Discussion

Loss of sensation around the incision for a total knee replacement has been frequently reported by patients and in the literature. However, the effects on clinical outcomes are unknown. There have been speculations that lack of sensation around a total knee incision may result in poor patient outcomes, difficulty with day-to-day activities such as kneeling, and overall worse patient satisfaction [[11], [12], [13], [14], [15],18].

This study demonstrated a high rate, 64.3%, of measured skin sensory disturbances around a total knee arthroplasty. This finding is supported by Lee et al. [4]. In this cadaveric study, infrapatellar branches of saphenous nerve were identified proximally to the tibial tubercle leading the authors to conclude that that there was no consistent way to preserve lateral skin innervation using a traditional midline approach. An interesting finding in our study was a statistical difference between longer incision length and numbness. Although we did not collect the specific location of the incision in relation to the tibial tubercle, this finding could be due to less distal dissection which would spare the infrapatellar branches of saphenous nerve.

The unknown effects of skin numbness have driven some surgeons to explore alternative approaches and minimally invasive techniques [3,7,15,19]. Tsukada et al. [15] demonstrated better kneeling ability and lower occurrence of skin numbness after an anterolateral approach than a traditional midline incision. Although the authors did not report any additional complications during their follow-up, long-term effects of an anterolateral approach are still unknown. Alternative approaches have not been thoroughly studied and may subject patients to unnecessary harm.

Despite a high rate of postoperative sensory disturbances, majority of the patients did not report having any subjective numbness. A similar finding demonstrated by a study by Black et al. [20] noted that patients that were informed about risks of postoperative numbness before surgery were more likely to self-report a lack of sensation. In our study, 20.6% of patients reported numbness, despite having intact sensation on monofilament testing. All patients underwent a formal consent process before proceeding with a total knee replacement during which potential damage to neurovascular structures was discussed. However, we cannot with certainty say whether issues with lateral skin numbness were specifically discussed. This further highlights that patients often have difficulty accurately determining skin sensation after the surgery.

When evaluating satisfaction rates, our study did not find any statistical difference between patients with intact sensation and those that were found to have deficits postoperatively. This is again in keeping with previous literature supporting no effect on PROMs [5,6,8].

Furthermore, our study demonstrated that only 11% of patients had issues with kneeling after surgery. This is significantly lower than the 50%-80% rate reported in the literature [6,[21], [22], [23]]. A large portion of our patients, 66.7%, answered “I cannot recall doing this activity” when asked about kneeling. We suspect that this cohort would contain a large number of patients that would have issues with kneeling. However, patients do not seem to encounter this problem, questioning the practical importance of kneeling for patients’ daily activities.

There are a few weaknesses in this study. Collected data were categorized during analysis to allow the authors to interpret the data and reach clinically relevant conclusions. Some of the power of the study may have been lost during this process. In addition, previously validated PROMs were not used as outcome measures. The authors felt that a simplified scale and a “yes” or “no” response would provide the necessary clinical information about patient satisfaction.

Conclusions

This study further highlights the high incidence of skin numbness after total knee arthroplasty. However, most patients may not be aware of this complication. Furthermore, objective sensory deficit around the incision does not affect patient satisfaction or ability to kneel after total knee arthroplasty.

Conflicts of Interest

The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: B. Lanting is a paid consultant for Stryker, DePuy, Smith and Nephew, and IntelliJoint; received research support from Stryker, DePuy, and Smith and Nephew; and received institutional support from Stryker, DePuy, Smith and Nephew, MicroPort, and Zimmer. S. MacDonald received royalties from DePuy and Johnson & Johnson Company; is a paid consultant for DePuy and Johnson & Johnson Company; has stock or stock options in JointVue, CurvaFix, Hip Innovations Technology, and PSI; received research support from Stryker, DePuy, Smith and Nephew, and Zimmer; and is a board member of the Canadian Orthopaedic Association and International Hip Society. D. Ross is a board member in the Canadian Society of Plastic Surgeons.