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Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Patients and methods.
  5. Results
  6. Discussion
  7. AUTHOR CONTRIBUTIONS
  8. REFERENCES

Objective

Vibratory perception threshold (VPT) is impaired in patients with knee osteoarthritis (OA). It is, however, not known if sensory deficits precede or follow as a consequence of OA. The aim of this study was to investigate VPT in 2 independent groups of patients with high risk of future OA (young anterior cruciate ligament [ACL]-injured patients and middle-aged meniscectomized patients) and compare them to age-matched controls.

Methods

VPT was assessed at the medial malleolus (MM) and medial femoral condyle (MFC) in 2 independent groups of patients and matched controls: ACL-injured patients (n = 39, mean ± SD age 24.0 ± 5.2 years, mean ± SD BMI 24.0 ± 2.9 kg/m2, mean ± SD time since injury 21.9 ± 21.6 months) and controls (n = 28, mean ± SD age 25.6 ± 4.4 years, mean ± SD BMI 23.6 ± 2.2 kg/m2), and meniscectomized patients (n = 22, mean ± SD age 49.6 ± 4.8 years, mean ± SD BMI 24.7 ± 2.7 kg/m2, mean ± SD time since surgery 49.6 ± 5.0 months) and controls (n = 25, mean ± SD age 49.4 ± 5.2 years, mean ± SD BMI 25.2 ± 4.9 kg/m2).

Results

ACL-injured patients had a better VPT than controls at the MM (P = 0.030), which persisted after adjusting for age and sex (P = 0.034). At the MFC, there was a similar trend in favor of ACL injured patients (unadjusted P = 0.093, adjusted P = 0.122). No differences were seen in VPT at the MM between meniscectomized patients and controls, whereas there was a tendency for better VPT in meniscectomized patients at the MFC (unadjusted P = 0.085, adjusted P = 0.092).

Conclusion

Impaired vibratory sensation could not be confirmed in 2 independent groups of patients compared to age-matched controls, suggesting that impaired vibratory sense is not present in knee-injured patients at high risk or in the very early phase of knee OA.


Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Patients and methods.
  5. Results
  6. Discussion
  7. AUTHOR CONTRIBUTIONS
  8. REFERENCES

Patients with knee osteoarthritis (OA) have impaired sensorimotor function (1–3). One component of sensorimotor function is proprioception (4). It remains unclear, however, whether sensory deficits precede OA or arise as its consequence. Hence, preexisting proprioceptive impairments may alter neuromuscular activity, reduce protective reflexes around the knee joint, and cause increased mechanical loading and subsequent damage leading to OA or, conversely, OA-mediated joint degeneration may lead to proprioceptive deficits (2).

Vibratory sense is a separate yet closely related sensory pathway to proprioception and they are transmitted in parallel through the dorsal columns of the spinal cord (5, 6) and share peripheral sensory bodies such as Pacinian corpuscles, which are involved in proprioception (i.e., through articular mechanoreception [4]) as well as in vibratory sense (5). A recent study reported impaired vibratory perception threshold (VPT) in patients with knee OA (7), and worse VPT has been observed in the upper and lower extremities in hip OA patients indicating a generalized sensory deficit in patients with OA (8). Assessment of VPT is a simple and reliable method to assess sensory deficits (7, 9) compared to methods to evaluate proprioception (i.e., joint position sense and kinesthesia), which are often criticized for poor reliability (4).

Patients with anterior cruciate ligament (ACL) and meniscus injuries have been reported to have proprioceptive deficits measured as impaired kinesthesia and joint position sense, respectively (10, 11). Young patients with previous ACL injuries are at high risk of knee OA (12). Furthermore, middle-aged patients with degenerative meniscus tears are suggested to be at particularly high risk of knee OA or have early changes of knee OA (13). As such, they represent 2 distinctly different groups of patients to study early factors involved in OA pathogenesis.

Knowledge on potential sensory deficits in patients at high risk or in the very early phase of OA is important since studies have indicated that such deficits may be counteracted by neuromuscular exercise and strength training (3). The aim of this study was to investigate the hypothesis that sensory deficits, measured as VPT, are present in patients at high risk or with very early changes of knee OA. To investigate this, we studied VPT in 2 independent groups of patients: young ACL-injured patients and middle-aged meniscectomized patients compared to age-matched controls.

Significance & Innovations

  • Sensory function, measured as vibratory perception threshold, has not previously been assessed in patients at high risk or with very early changes of knee osteoarthritis.

  • The hypothesized sensory deficits could not be confirmed in patients with anterior cruciate ligament injury or in patients with a degenerative meniscal tear.

  • These findings indicate that sensory function, measured as vibratory perception threshold, is not impaired in patients at high risk or in the very early phase of knee osteoarthritis.

Patients and methods.

  1. Top of page
  2. Abstract
  3. Introduction
  4. Patients and methods.
  5. Results
  6. Discussion
  7. AUTHOR CONTRIBUTIONS
  8. REFERENCES

A convenience sample of patients and controls from 2 separate studies were analyzed in the present study. ACL-injured patients (ACL group) and their controls (ACL-C group) were from Lund, Sweden and meniscectomized patients (APM group) and their controls (APM-C group) were from Odense, Denmark.

ACL and ACL-C groups.

Thirty-nine ACL-injured patients participating in supervised neuromuscular training were enrolled at a physiotherapy clinic. Inclusion criteria were age 18–35, ongoing postinjury/postsurgery training, ≥10 weeks after ACL injury or ≥16 weeks after ACL reconstruction, ability to perform a single-leg hop, and self-reported functional limitations. Functional limitations were determined as knee-related problems in physical function and/or quality of life in at least 2 of 4 questions in the Knee Injury and Osteoarthritis Outcome Score (KOOS) sport and recreation function and quality of life subscales (questions 3 and 4 of the KOOS). Exclusion criterion was a history of major orthopedic lesions such as fracture or knee injury other than their ACL injury. Twenty-eight age-matched controls (14) were recruited among students at the Faculty of Medicine, Lund University and staff members at Malmö University Hospital. Exclusion criterion was a history of major orthopedic lesion (i.e., knee injury or fracture).

APM and APM-C groups.

Patients were initially recruited 1–2 years after an arthroscopic partial medial meniscectomy through the surgical code system from 2 different hospitals (15). Patients were 35–55 years of age at the time of surgery to include a majority of patients with degenerative meniscus tears. Exclusion criteria were previous knee ligament injury, severe cartilage changes defined as deep clefts or visible bone at meniscectomy, and self-reported comorbidities limiting participation in the study. Age-matched controls from the same geographic area as the patients were identified through the Danish Civil Registration System. Exclusion criteria were previous knee surgery and/or ligament injury and self-reported comorbidities limiting participation in the study. The patients and controls included in this study participated in a followup assessment 4 years postoperatively. In total, 31 patients and 31 controls were recruited at the initial assessment 2 years postoperatively; of these, 22 patients and 25 controls agreed to return for a followup assessment 4 years postoperatively where VPT was assessed.

None of the patients or controls self-reported diabetes mellitus or other neurologic disorders that could affect the VPT measurements. All subjects provided written informed consent and the studies were approved by the ethics committee of Lund University, Sweden and of the Region of Southern Denmark, respectively.

Self-reported outcomes.

The KOOS (16), a valid patient-reported outcome measure for use in patients with ACL injuries or meniscus tears (16, 17), was used to assess knee-related pain, symptoms, function during activities of daily living and sport and recreation, as well as quality of life. A normalized score is calculated for each subscale (where 0 indicates extreme symptoms and 100 indicates no symptoms).

VPT.

VPT was assessed using a biothesiometer (Bio-Medical Instrument Comany) (9) at 2 sites (the most prominent point of the medial malleolus [MM] and the medial femoral condyle [MFC]), according to previously described methodology (14). Prior to testing, the biothesiometer was demonstrated on the patient's styloid process of the hand for familiarization. During testing, the biothesiometer tip was held with uniform pressure while the subjects lay in a supine position with their eyes closed concentrating on their foot/knee and responded to the first instant of any sensation of vibration. Three consecutive measurements were taken at each site without moving the tip of the biothesiometer. The amplitude was increased by 1 volt/second until the subjects responded to a sensation of vibration. This was noted as the VPT (i.e., a higher value indicates worse VPT). The amplitude was reduced to 0 between each of the 3 consecutive measurements. The first measurement was regarded as a trial test and was excluded from the analysis. If the difference between the second and third measurement was above 20%, 2 additional tests were conducted. The mean of the second and third (or fourth and fifth) measurements was used in the analysis. High reliability has previously been reported for the biothesiometer in patients with knee OA (intraclass correlation coefficient [ICC] 0.96–0.99) (7) as well as for healthy subjects (9). Additionally, test–retest reliability was found to be high also in the current study when assessed in 10 healthy subjects from the APM-C group (ICC 0.84–0.90).

Statistical analysis.

Student's unpaired t-test and chi-square test were used as appropriate to compare subject characteristics and VPT between patients and controls (i.e., the ACL versus ACL-C and APM versus APM-C, respectively). In addition, a linear regression analysis was performed to evaluate the effect of age and sex on the VPT results. For the linear regression analysis, data were log transformed if they did not follow Gaussian distribution. Mann-Whitney test was used to assess differences in KOOS scores between patients and controls. Stata 11.0 (StataCorp) was used for all statistical analyses, using a prespecified level of significance of 0.05.

Results

  1. Top of page
  2. Abstract
  3. Introduction
  4. Patients and methods.
  5. Results
  6. Discussion
  7. AUTHOR CONTRIBUTIONS
  8. REFERENCES

The characteristics of participants are shown in Table 1. The mean ± SD time since ACL injury was 21.9 ± 21.6 months. Twenty-four subjects had an ACL reconstruction (hamstring tendon graft, mean ± SD time since surgery 13.9 ± 19.3 months) and 15 subjects were treated with rehabilitation only. There were no differences in subject characteristics, KOOS, or VPT values between those patients who underwent reconstruction (n = 24) and those who did not (n = 15), consequently they are reported as one group. Mean ± SD time since meniscectomy in the APM group was 49.6 ± 5.0 months.

Table 1. Subject characteristics*
 ACL (n = 39)ACL-C (n = 28)PAPM (n = 22)APM-C (n = 25)P
  • *

    Values are the mean ± SD unless otherwise indicated. ACL = anterior cruciate ligament (ACL)-injured patients; ACL-C = controls to ACL-injured patients; APM = meniscectomized patients; APM-C = controls to meniscectomized patients; BMI = body mass index; KOOS = Knee Injury and Osteoarthritis Outcome Score; ADL = activities of daily living; Sport/rec = sport and recreational function; QOL = quality of life.

  • Difference between groups (i.e., ACL versus ACL-C and APM versus APM-C) assessed using unpaired t-test.

  • Difference in distribution of males/females between groups assessed using chi-square test.

  • §

    Difference between groups in KOOS subscales assessed using Mann-Whitney test.

Age, years24.0 ± 5.225.6 ± 4.40.17849.6 ± 4.849.4 ± 5.20.893
BMI, kg/m224.0 ± 2.923.6 ± 2.20.50524.7 ± 2.725.2 ± 4.90.636
Sex (male/female, no.)20/1914/140.91817/514/110.125
KOOS scores§      
 Pain79.8 ± 11.498.8 ± 2.90.00090.1 ± 13.396.2 ± 4.70.079
 Symptoms72.6 ± 13.098.5 ± 3.90.00090.7 ± 10.095.1 ± 5.50.084
 ADL90.0 ± 9.499.9 ± 0.60.00094.6 ± 9.498.1 ± 3.20.183
 Sport/rec46.8 ± 22.698.2 ± 3.90.00084.1 ± 20.891.6 ± 10.50.319
 QOL40.5 ± 11.495.9 ± 6.30.00078.8 ± 16.890.0 ± 13.50.007

The ACL group had significantly better VPT values than the ACL-C group at the MM, which persisted when adjusting for age and sex, and a trend for better VPT was observed at the MFC (Table 2). No differences were seen in VPT at the MM between the APM and APM-C groups, whereas there was a trend for better VPT on the MFC in the APM group (Table 3). Comparing the 2 control groups showed that the younger group (ACL-C) had better VPT than the middle-aged group (APM-C) (P = 0.001 and P = 0.021 for MM and MFC, respectively).

Table 2. Vibration perception thresholds in young anterior cruciate ligament (ACL)-injured patients and controls*
 ACL-injured (n = 39)Controls (n = 28)DifferencePAdjusted P
  • *

    Values are the mean (95% confidence interval) volts unless otherwise indicated.

  • Unpaired t-test.

  • Linear regression adjusted for age and sex.

Medial malleolus9.4 (8.6, 10.3)11.0 (9.7, 12.3)−1.6 (−3.1, −0.2)0.0300.034
Medial femoral condyle15.7 (14.0, 17.5)18.1 (15.8, 20.4)−2.4 (−5.1, 0.4)0.0930.122
Table 3. Vibration perception thresholds in middle-aged meniscectomized patients and controls*
 Meniscectomized (n = 22)Controls (n = 25)DifferencePAdjusted P
  • *

    Values are the mean (95% confidence interval) volts unless otherwise indicated.

  • Unpaired t-test.

  • Linear regression adjusted for age and sex.

Medial malleolus14.4 (12.2, 16.6)16.6 (13.6, 19.6)−2.2 (−6.0, 1.5)0.2350.182
Medial femoral condyle18.9 (15.9, 21.9)23.0 (19.3, 26.8)−4.1 (−8.9, 0.6)0.0850.092

Discussion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Patients and methods.
  5. Results
  6. Discussion
  7. AUTHOR CONTRIBUTIONS
  8. REFERENCES

To our knowledge, this is the first study to evaluate vibratory sense in patients at high risk or in the very initial phase of OA development. The present study failed to demonstrate impaired vibratory sensation in 2 independent groups of patients compared with controls, indicating that vibratory sense is not impaired in knee-injured patients at high risk of or in the very early phase of knee OA.

Impaired somatosensory function, measured as poor joint position sense, abnormal kinesthesia, and decreased vibratory sense, has been observed in patients with knee OA (2, 7). In this study, we evaluated VPT, a quantifiable and reliable measure of sensory sensation. The sensation of vibration is distinct from proprioceptive acuity; however, they are both involved in stereognosis and are conducted through adjacent pathways in the dorsal columns of the spinal cord (5, 6). The presence of impaired vibratory sensation could not be confirmed in the injured knee joint or in the ankle in these 2 independent groups of knee-injured patients compared to age-matched controls. This indicates that neither joint-specific nor generalized impairments in vibratory sense are present in knee-injured patients at high risk or in the very early phase of knee OA. This was in contrast to previous studies showing proprioceptive deficits in similar patients (10, 11), which may indicate that VPT and measures of position sense and kinesthesia, although related, are not identical concepts. In fact, the trend of the data, particularly for the ACL-injured patients, suggested that VPT might be better in these patients at high risk of OA, relative to controls. The reason for this trend is unknown and subject to future study, but could relate to increased physical activity, and therefore injury risk, among those with greater sensory function.

In this study, we examined knee-injured patients who may have a different pathophysiologic pathway to knee OA than individuals developing knee OA without known prior knee injury. Therefore, the findings from this study cannot be extrapolated to other groups of noninjured patients at risk of knee OA and it is possible that sensory deficits may play a role for these patients in the development of OA.

Several studies have previously shown impaired sensory function, measured as joint position sense and threshold for detection of knee joint displacement (kinesthesia) (2, 3, 18), with increasing age, which was further impaired in older patients with knee OA. Even though we did not find the hypothesized impairment in VPT in patients compared with controls, a significant difference was seen in VPT between the young (ACL-C) and middle-aged (APM-C) control groups confirming that vibratory sense, as proprioception, is reduced with age. In addition, worse VPT values have been reported for the proximal compared to the more distal measurement sites (7, 8, 19). This was also observed in the present study, as VPT values consistently were better at the MM compared to the MFC.

The present study was conducted on a convenience sample from 2 different cohorts. Thus, recruitment could not be adjusted to a specific power calculation. We hypothesized that patients would have worse VPT than controls (i.e., higher VPT values). According to the concept of equivalence testing (20), the upper limit of the confidence interval of the difference between groups represents the maximum likely difference in favor of our hypothesis (i.e., patients having worse VPT than controls) if repeating the experiment. Therefore, it is unlikely that the lack of a difference in favor of the hypothesis is due to a type II error. Furthermore, the trend of patients having better VPT values than controls was consistent in both groups independently.

Radiographs were not taken, and it is therefore not possible to describe the degree of knee OA–associated structural changes in patients or controls. Given their young age, it is unlikely that ACL patients had substantial structural changes. Furthermore, it is unlikely that meniscectomized patients had structural changes visible on radiographs, since only patients without severe cartilage changes defined as deep clefts or visible bone reported in the perioperative report were included. In addition, KOOS scores were considerably better in these ACL-injured and meniscectomized patients than in patients diagnosed with knee OA. The young and middle-aged controls self-reported no or very minor pain or functional reductions, making the presence of OA also very unlikely in these groups.

In conclusion, impaired vibratory sensation could not be confirmed in 2 independent groups of patients compared to age-matched controls, suggesting that impaired vibratory sense is not present in knee-injured patients at high risk or in the very early phase of knee OA.

AUTHOR CONTRIBUTIONS

  1. Top of page
  2. Abstract
  3. Introduction
  4. Patients and methods.
  5. Results
  6. Discussion
  7. AUTHOR CONTRIBUTIONS
  8. REFERENCES

All authors were involved in drafting the article or revising it critically for important intellectual content, and all authors approved the final version to be published. Mr. Thorland had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.

Study conception and design. Thorlund, Shakoor, Block, Roos.

Acquisition of data. Ageberg, Sandal.

Analysis and interpretation of data. Thorlund, Shakoor, Block.

REFERENCES

  1. Top of page
  2. Abstract
  3. Introduction
  4. Patients and methods.
  5. Results
  6. Discussion
  7. AUTHOR CONTRIBUTIONS
  8. REFERENCES
  • 1
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