Abstract
Background
Common peroneal nerve palsy (CPNP) is a rare complication of total knee arthroplasty (TKA). It may lead to impaired function and pain. The purpose of this study was to determine the frequency and outcome of CPNP in a single orthopedic unit and to identify potential risk factors.
Methods
This is a single-center study using the hospital’s prospectively collected quality registry. All TKAs from 2002 to 2022 were included and followed up from 3 to 24 months with a follow-up rate of 98.4%. The local joint register was reviewed to identify patients with CPNP and used to extract data regarding the operation and the patients with and without CPNP. The groups were compared to identify possible risk factors for nerve injury. The medical records of the patients with CPNP were reviewed to determine the CPNPs’ severity and outcome, and their preoperative radiographs were analyzed and compared to a control group with no nerve injury.
Results
A total of 7704 TKAs were included, and 25 CPNPs were identified (0.32%). Complete palsies occurred in 18 cases, and partial palsies in 7. Postoperative epidural anesthesia, preoperative excessive valgus, and female sex were significant risk factors. Body mass index and age were not associated with CPNP. Two-thirds of the complete palsies had complete recovery, and four-fifths of the partial palsies recovered.
Conclusions
The incidence of CPNP was 0.32%, and risk factors were epidural anesthesia, excessive valgus, and female sex. Most patients with CPNP recovered completely. Partial palsies had better outcomes than complete palsies in our cohort.
Keywords: Total knee arthroplasty, Common peroneal nerve palsy, Epidural, Recovery, Outcome
Introduction
Common peroneal nerve palsy (CPNP) is the most common nerve injury after total knee arthroplasty (TKA) with an incidence rate of 0.12%-0.53% [[1], [2], [3], [4]]. Most nerve injuries following TKA are neuropraxia, where the myelin sheath of the nerve is damaged. The axon itself is unharmed, and when the myelin sheath is healed, nerve function is likely to recover. Should axonotmesis happen, the nerve pathway will be disrupted, and the prognosis is more severe, but full recovery may still occur. Neurotmesis is the most severe form of nerve injury and involves complete disruption of the myelin sheath and axon and, even with microsurgical intervention, carries the worst prognosis [5]. The peroneal nerve has less connective tissue and fewer large funiculi than the tibial nerve, making its axon more susceptible to injury from traction when correcting a deformity [6].
Not all patients with CPNP recover completely, and some will suffer persistent muscle weakness and/or annoying dysesthesia [4]. The peroneal nerve is more susceptible to injury than the tibial nerve due to anatomical features. As it curves around the fibular neck, it is more prone to injury from compression from hematoma formation or external compression and from stretching during restoration of the mechanical axis. In addition to preoperative valgus deformities, previous spinal pathology, postoperative epidural anesthesia (EDA), and prolonged tourniquet inflation time have also been linked to peroneal nerve injury [2,5]. Treatment of CPNP is mainly conservative. Reported series of surgical decompression of CPNP are few, making it difficult to draw conclusions about its efficacy [7].
Material and methods
Study design
The study was a quality-assurance study performed as part of ongoing quality surveillance in the hospital’s orthopedic department and was approved by the hospital’s data-protection official. It was retrospective, and prospectively collected data from the department’s quality registry were used. The cohort consisted of all consecutive TKA performed at a single orthopedic department between 2002 and 2022. The department’s joint replacement registry, which includes all complications that occur within 3 months of surgery, was retrospectively reviewed to identify patients with nerve palsies. Of the cohort participants, 98.4% attended the 3-month follow-up and are thus included in this registry and analysis.
Patients
All 7704 patients in a single orthopedic unit having primary or revision TKA between 2002 and 2022 and attending the 3-month follow-up were eligible for the study and included. Of the total, 7128 underwent primary TKA, and 576 were revisions. Of the cohort, 4931 were female (64%), and 2773 were male (36%). No patient with nerve palsy had previous open-knee surgery, and all were diagnosed with primary osteoarthritis.
Surgical procedures
The primary TKAs were fully cemented in 734 (10.3%) cases, cementless in 4 (0.056%) cases, and hybrid (cemented tibia/cementless femur) in 6390 (89.6%) cases. Profix or Legion total knee prostheses (Smith & Nephew, Memphis, TN) were used in all cases. All patients were operated using the medial parapatellar approach with or without patellar resurfacing. Of the total, 6390 (89.6%) TKAs were cruciate-retaining with hybrid fixation (cementless femoral component and cemented tibial component), and 734 (10.3%) TKAs were posterior-stabilized with a patellar component and all components cemented. Routine use of tourniquet was discontinued in 2016, and after 2015, spinal anesthesia was used more often than EDA.
Clinical and radiographic evaluation
Demographic data, body mass index (BMI), American Society of Anesthesiologists score, operation time, and type of anesthesia were automatically extracted from the quality register for all included patients.
Preoperative long-standing anteroposterior and lateral radiographs were evaluated for all patients with nerve injury, and the anatomical tibiofemoral axis was measured. To analyze alignment deformity as a potential risk factor for CPNP in primary TKA, we also evaluated the radiographs of a sample of TKA patients without nerve injury and compared the alignment in the 2 groups. Alignment was considered normal if the deviation was between 0° and 5°, moderate valgus was between 6° and 11°, and excessive valgus was 12° or more [1].
Peroneal nerve palsies were classified as complete or partial. A complete palsy was defined as no dorsiflexion at all the toes or ankles and partial palsy as weakness of dorsiflexion [1,6].
Tourniquet pressure and inflation time were collected from the medical records for the CPNP patients.
Follow-up
Any peroneal nerve palsy that had not resolved at 3 months postoperatively was followed further. The mean follow-up duration was 12 months, with a range of 3 months to 2 years. For some patients, the nerve injury was confirmed by electromyography. At each follow-up visit, the clinical status of the peroneal nerve function was recorded.
Statistical analysis
Group comparisons of continuous variables between patients with and without CPNP were performed using Student's t-test for independent samples. These variables were reported as means and standard deviations. Discrete variables were compared using chi-square test or Fisher’s exact test and reported as frequencies and percentages. Multiple logistic regression was used to control for confounding factors. Adjusting for the matching variables is recommended when performing a matched case control study [8]. A P value of less than .05 was considered statistically significant. Odds ratios (OR) were also reported to quantify the magnitude of the associations. Analyses were performed using the statistical package R, version 4.0.3.
Results
Of the 7704 TKAs included in the study, 25 (0.32%) had CPNP. The characteristics of the patients with CPNP and the control patients are shown in Table 1. Patients with CPNP were significantly more likely to be women (P = .036), to have postoperative EDA (P < .001), and to be operated with a tourniquet (P = .013) than controls. The operation time was also longer in the CPNP group (P = .025). Mean age and BMI and the distribution of American Society of Anesthesiologists scores and revision operations were similar in the 2 groups (Table 1).
Table 1.
Characteristics of patients with CPNP compared to control patients after TKA.
| Variable | CPNP patients (n = 25) | Control patients (n = 7679) | P value (odds ratio) |
|---|---|---|---|
| Age (mean, SD) | 69.6, 9.5 | 69.2, 9.1 | .84 |
| BMI (mean, SD) | 28.1, 5.1 | 28.8, 4.8a | .49 |
| Revisions (n, %) | 3, 12% | 573, 7.5% | .39 |
| Females (n, %) | 21, 84% | 4902, 64% | .036 (2.97) |
| ASA (mean, SD) | 2, 0.5 | 2.11, 0.54b | .29 |
| ASA (n, %) | .77 | ||
| ASA 1 | 3, 12% | 632, 10%b | |
| ASA 2 | 19, 76% | 4649, 70%b | |
| ASA 3 | 3, 12% | 1319, 20%b | |
| ASA 4 | 0, 0% | 14, 0.2%b | |
| Operation time in min (mean, SD) | 92, 37 | 74, 27c | .025 |
| Epidural catheter (n, %) | 20, 80% | 2720, 37%c | <.001 (6.68) |
| Use of tourniquet (n, %) | 21, 84% | 4583, 60% | .013 (3.54) |
| Tourniquet time in min (mean, SD) | 82, 31d | ||
| Tourniquet time ≥120 min (n, %) | 3, 14.3%d | ||
| Tourniquet pressure in mmHg (mean, SD) | 270, 16d | ||
| FTA (mean, SD) | 11.4, 10.4e | ||
| <6° (n, %) | 7, 32%e | ||
| 6°-11° (n, %) | 4, 18%e | ||
| >11° (n, %) | 11, 50%e |
ASA, American Society of Anesthesiologists; FTA, femorotibial angle.
n = 5909 for control BMI.
n = 6614 for control ASA.
n = 7265 for control operation time.
n = 21 for CPNP tourniquet variables.
n = 22 for CPNP FTA.
Of the 7128 primary TKAs, 22 (0.31%) had CPNP. Of these 22 with CPNP, 15 had preoperative valgus anatomic alignment: 4 in moderate valgus (6°-11°) and 11 in excessive valgus (≥12°). Of the remaining 7 primary TKAs with CPNP, 5 had normal alignment (0°-6° valgus), and 2 were in varus (4° and 10°). Six primary TKA patients with CPNP had spinal anesthesia and no EDA: Five of these had excessive valgus, and 1 had moderate valgus. Only 1 patient had documented diabetes mellitus. No patient had rheumatoid arthritis, previous spine surgery, or known damage of the sciatic nerve before TKA.
Among the 21 patients with CPNP operated with the use of tourniquet, 3 patients had a tourniquet time of 120 minutes or more. Tourniquet time and pressure for the patients with CPNP are summarized in Table 1.
To analyze the effect of preoperative alignment as a potential risk factor, the 22 primary TKA patients with CPNP were compared to a control sample of 44 patients without nerve injury. The control patients were matched regarding the use of EDA, gender, age, and year of operation, and the groups were similar with respect to potential confounders (Table 2). However, there were significantly more patients with excessive valgus (≥12°) in the CNPN group (Table 2). The crude OR for sustaining CPNP with excessive valgus was 6.1 (95% CI 1.6-25.3, P = .003). When adjusting for sex, the use of EDA, and the use of tourniquet, the OR was 9.59 (95% CI 2.51-48.1, P = .002).
Table 2.
Characteristics of primary TKA patients with CPNP compared to a sample of matched control patients.
| Variable | CPNP patients (n = 22) | Matched control patients (n = 44) | P value (odds ratio) |
|---|---|---|---|
| Age (mean, SD) | 71, 8 | 72, 8 | >.9 |
| BMI (mean, SD) | 27.6, 4.8 | 28.6, 4.5 | .4 |
| Females (n, %) | 19, 86% | 38, 86% | >.9 |
| ASA (n, %) | .4 | ||
| ASA 1 | 3, 14% | 2, 4.5% | |
| ASA 2 | 16, 73% | 37, 84% | |
| ASA 3 | 3, 14% | 5, 11% | |
| Epidural catheter (n, %) | 17, 77% | 34, 77% | >.9 |
| Use of tourniquet (n, %) | 18, 82% | 36, 82% | >.9 |
| Tourniquet time in min (mean, SD) | 76, 28 | 59, 14 | .005 |
| Tourniquet pressure in mmHg (mean, SD) | 271, 16 | 271, 11 | .8 |
| FTA (mean, SD) | 11, 10 | 4, 8 | .004 |
| <6° (n, %) | 7, 32% | 28, 64% | |
| 6°-11° (n, %) | 4, 18% | 10, 23% | |
| >11° (n, %) | 11, 50% | 6, 14% | .003 (6.1) |
ASA, American Society of Anesthesiologists; FTA, femorotibial angle.
Of 576 revision TKAs, 3 patients (0.52%) had a peroneal nerve injury, and all 3 had postoperative EDA. Two of these patients had drop foot only. The first patient had revision for arthrofibrosis, and the tibial nerve was affected in addition to drop foot. This patient's tourniquet pressure was 270 mmHg for 108 minutes during the revision. The second patient was diagnosed with compartment syndrome the second day after surgery and underwent fasciotomy of all 4 compartments. Tourniquet pressure during the revision surgery was 265 mmHg for 102 minutes. The patient had almost full recovery after 18 months. The third patient also had postoperative EDA, and a tourniquet pressure of 250 mmHg for 151 minutes. This patient was followed up for only 6 months due to severe comorbidity. No sign of nerve recovery was seen at the last follow-up.
Recovery from CPNP
There were 18 complete palsies, of which 11 (61%) had full recovery. Time to full recovery varied from 6 to 24 months, with a mean of 15 months. In addition, 6 of the complete palsies had partial recovery, and 1 showed no sign of improvement at their latest follow-up, which was at 6 months due to their deteriorating health.
There were also 7 partial palsies, of which 6 (86%) had full recovery. Time to full recovery varied from 3 to 24 months, with a mean of 11 months. The remaining patient suffered from annoying dysesthesia at their latest follow-up. This patient had revision TKA due to arthrofibrosis, and both the tibial and peroneal nerve were affected. In addition to dysesthesia, the patient’s range of movement was between 50º and 90º. The patient had their leg amputated 5 years later and ended up very pleased with a technically-advanced prosthesis.
No patients with CPNP had neurolysis of the peroneal nerve.
Discussion
The incidence rate of CPNP in this study was 0.32%, which coincides with the findings of 1 systematic review reporting a mean incidence of 0.4% (range 0.3%-4.3%) [4]. An important risk factor for CPNP in our study was postoperative EDA (Table 1). Park et al. [1] and Horlocker et al. [9] found no significant correlation between CPNP and EDA, while Idusuyi and Morrey [10] and Beller et al. [11] found EDA to be a significant risk factor. We believe the mechanism may be loss of sensation, proprioception, and sometimes loss of motor control making the nerve more prone to trauma from external compression. This is supported by the fact that CPNP also may occur after closed manipulation under anesthesia for stiff TKAs, when EDA is used. We have identified 3 such cases in our quality registry. CPNP has even been reported after EDA for relieving pain after abdominal surgery [12].
Preoperative valgus deformity has also been found to be a risk factor for CPNP by several authors [10,13]. Christ et al. in their study of 383,060 cases found preoperative valgus to be a significant risk factor for nerve injury (OR = 4.19, P < .0001) [2]. In our study, the OR was found to be even higher than this, but with wide confidence intervals. It is likely that by eliminating 1 important risk factor by using EDA less frequently, the relative importance of excessive valgus as a risk factor will be more important. In this regard, it is noteworthy that in 5 of 6 CPNP patients where EDA was not used, there was excessive valgus preoperatively. Interestingly, the alignment distribution in the control group of this study is similar to that found in a previous study performed at our institution that included an unselected group of TKA patients [14]. Park et al. also noted more valgus deformities in their CPNP group than in the control group, but the difference did not reach statistical significance [1].
In our cohort, 19 of the 22 primary TKAs with CPNP were done under tourniquet. All these patients also had EDA. Two patients had tourniquet time more than 120 minutes, which is above the accepted time limit. If the tourniquet pressure is kept below 300 mmHg for less than 120 minutes, most studies do not find tourniquet to be a significant risk factor [1,10,15]. Thus, the 17 of these 19 palsies where both time and pressure were kept within accepted limits were unlikely to have been caused by the use of tourniquet.
Christ et al. found hypothyroidism to slightly increase the risk for CPNP [2]. It is interesting that as many as 6 of our 25 cases of CPNP had hypothyroidism. In addition, 4 of these 6 were in valgus. Contrary to the findings of Park et al. [1], we did not find age and BMI to be significant risk factors (Table 1). However, the female patients in our study had increased risk of CPNP, like Christ et al. found in their large study of 383,060 cases [2].
The clinical course of the CPNP cases in our study indicates a better outcome for partial palsies than for complete palsies. Among the 7 with partial palsies, 6 (86%) had full recovery, whereas only 11 (61%) of the 18 with complete palsies regained normal function. Time to full recovery ranged from 6 to 24 months (mean 15 months) for those with complete CPNP and from 3 to 24 months (mean 11 months) for those with partial CPNP.
As soon as CPNP is diagnosed after TKA, the hip and knee should be placed in 20°-30° of flexion, and dressing should be removed to ensure less stretch and compression of the nerve.
Any hematoma suspected of compressing the nerve should be evacuated. The question of whether surgical release of the CPNP is beneficial remains unresolved. Some advocate neurolysis if no clinical improvement is seen within 3 months [7,16]. Others would not explore the nerve unless there is a specific cause that could be relieved by surgery [1]. Rose et al. reported on 5 patients who underwent prophylactic decompression of peroneal nerve at the time of TKA [17], but all 5 developed CPNP.
This study has several limitations and strengths. It is a relatively large cohort of patients, and the data are from a single orthopedic unit, which reduces sources of variation related to the surgical protocol and patient population but may also limit the generalizability of the findings. The inclusion rate was very high (98.4%), and no patients with CPNP were lost to follow-up. Even though CPNP was recorded at the follow-up visits, the medical notes were studied retrospectively, introducing potential bias regarding the quality of recording the clinical course of the CPNP.
Conclusions
CPNP after TKA is a rare event. We found postoperative EDA, preoperative excessive valgus, and female sex to be risk factors. After complete CPNP, almost two-thirds recovered completely, and after partial palsy, four-fifths had full recovery. Unless a hematoma is present, therapy consists of flexion of hip and knee and relieving any tight dressing. If no sign of recovery is noticed after 3 months, neurolysis may be considered.
Conflicts of interest
The authors declare there are no conflicts of interest.
For full disclosure statements refer to https://doi.org/10.1016/j.artd.2024.101331.
CRediT authorship contribution statement
Øystein Høvik: Conceptualization, Data curation, Writing – original draft. Kjersti Kaul Jenssen: Data curation, Methodology, Writing – review & editing. Einar Amlie: Data curation, Project administration. Einar Andreas Sivertsen: Conceptualization, Data curation, Formal analysis, Methodology, Software, Writing – review & editing.
Acknowledgments
The authors thank Caryl Gay, MS, PhD, Lovisenberg Diaconal Hospital, Oslo, Norway, for proofreading the manuscript.
Appendix A. Supplementary data
References
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