Total Hip Arthroplasty (THA) surgery is a physical and cognitive challenge for surgeons. Data on stress levels, cognitive and physical load of orthopaedic surgeons, as well as ergonomic impact, are limited. With and without the use of an automated impaction device, operational efficiency and the surgeon's ergonomic, mental, and physical load was investigated. In a total of thirty THA procedures, a standard manual technique was compared with an automated impaction device. Three computerized cognitive tasks (Simon, pattern comparison, and pursuit rotor) and five physical tests (isometric wall-sit, plank-to-fatigue, handgrip, supra-postural task, and shoulder endurance) were used to assess psychophysiological load of the surgeon. Surgeon's cortisol concentration was evaluated from saliva samples. Postural risk was assessed by Rapid Upper Limb Assessment (RULA) and Rapid Entire Body Assessment (REBA). Efficiency was assessed by timing surgical steps and instrumentation flow. Cognitive performances after automated impaction showed faster response times and lower error rates with a greater time-on-target (+1.5 s) and a lower mouse deviation from target (−1.7 pixels). Manual impaction showed higher physical exhaustion in the isometric wall-sit test (10.6% vs. 22.9%), plank-to-fatigue (2.2% vs. 43.8%), the number of taps in the supra-postural task (−0.7% vs. −7.7%), handgrip force production in the dominant (−6.7% vs. −12.7%) and contralateral hand (+4.7% vs. +7.7%), and in shoulder endurance (−15s vs. −56s). An increase of 38.2% in salivary cortisol concentration between the midday (1.31 nmol/l) and afternoon session (1.81 nmol/l) was observed with manual impaction. After using automated impaction, salivary cortisol concentration decreased (−51.2%). Manual broaching time was on average 6′20’’ versus 7’3’’ with automated impaction. RULA of manual impaction scored 6 for cup impaction and 5 for femoral broaching, versus 3 and 3 for automated impaction, respectively. REBA of manual impaction scored 9 for cup impaction and 5 for femoral broaching, versus 4 and 3 for automated impaction, respectively. Automated impaction lowers surgeons’ cognitive and physical fatigue and leads to reduced stress and improved ergonomics without loss of surgical efficiency

Introduction. Alignment of the acetabular cup and femoral components directly affects hip joint loading and potential for impingement and dislocation following total hip arthroplasty (THA) [1]. Changes to the lines of action and moment generating capabilities of the muscles as a result of component position may influence overall patient function. The objectives of this study were to assess the effect of component placement on hip joint contact forces (JCFs) and muscle forces during a high demand step down task and to identify important alignment parameters using a probabilistic approach. Methods. Three patients following THA (2 M: 28.3±2.8 BMI; 1 F: 25.7 BMI) performed lower extremity maximum isometric strength tests and a step down task as part of a larger IRB-approved study. Patient-specific musculoskeletal models were created by scaling a model with detailed hip musculature [2] to patient segment dimensions and mass. For each model, muscle maximum isometric strengths were optimized to minimize differences between model-predicted and measured preoperative maximum isometric joint torques at the hip and knee. Baseline simulations used patient-specific models with corresponding measured kinematics and ground reaction forces to predict hip JCFs and muscle forces using static optimization. To assess the combined effects of stem and cup position and orientation, a 1000 trial Monte Carlo simulation was performed with input variability in each degree of freedom based on the ±1 SD range in component placement relative to native geometry reported by Tsai et al. [3] (Figure 1). Maximum confidence bounds (1–99%) were predicted for the hip JCF magnitude and muscle forces for three prime muscles involved in the task (gluteus medius, gluteus minimus and psoas). HJC confidence bounds were compared to Orthoload measurements from telemetric implants from 6 patients performing the step down task. Sensitivity of hip JCF and muscle force outputs was quantified by Pearson Product-Moment correlation between the input parameter and the value of each output averaged across four points in the cycle. Results. Variation in the placement of the stem and cup produced an average maximum confidence bound (1–99%) in hip JCF of 277.7±91.1N and forces of 259.4±58.3N in the gluteus medius for all three patients (Figure 2). Sensitivity to cup and stem placement varied among the three patients; however, in general, hip JCFs were more sensitive to the position of the stem than the cup (Figure 3). Hip JCF was most sensitive to stem anteversion (0.64±0.10) and the superior/inferior stem position (0.42±0.19). Discussion. Variation in stem anteversion and medial/lateral cup position contributed the largest amount of variability in hip JCF and muscle forces during a step down task. The probabilistic analysis characterized bounds for output parameters, considering interactions between alignment parameters. Alignments that avoid increases in JCF and muscle loading during high demand tasks may lead to earlier recovery of function, by reducing muscle fatigue and the need to develop compensatory movement patterns. Acknowledgements. This research was supported in part by DePuy-Synthes

Objectives

The aim of this study was to systematically review the literature on measurement of muscle strength in patients with femoroacetabular impingement (FAI) and other pathologies and to suggest guidelines to standardise protocols for future research in the field.

We present 2 year results of a prospective natural history study of Type III Acromioclaviclular joint dislocation (ACJD) treated non-operatively. Previous natural history studies are compromised by inconsistent definitions of the grade of injury and non-validated scoring tools; they do not identify which patients will have ongoing symptoms. This trial documents the strength and subjective recovery over time, and identifies risk factors for poor outcome and need for surgery. Patients with Rockwood Type III ACJD received a standardised rehabilitation protocol (6 sessions of physiotherapy). Clinical assessment was performed at presentation, 3, 6, 12 and 24 months after injury, including isometric strength testing, pain (VAS/10) and subjective scores – Subjective percentage of normal (SPON), American Shoulder and Elbow (ASES), Oxford Shoulder Score (OSS) and Quick Disabilities of Arm Shoulder and Hand (qDASH). 28 male patients were recruited, 26 reached 12, and 9 to 24 months follow up. Two required surgery and one emigrated. The mean age was 39 (15 to 67). Initial mean pain was 3/10, SPON 51% (6–95) and strength was 76% of the other side. By 3 months mean subjective recovery was 70% and strength 90%. Strength recovered to 99% of normal by 12 months but subjective scores remained at mean 90%; by 24 months subjective scores were mean 94%. 2 patients had subjective scores <80%. There was a wide range of initial subjective scores and weakness after Type III ACJD. 95% of strength had recovered by 6 months and subjective scores recovered to 94% of normal by 24 months. 4 patients (14%) did poorly with 2 requiring surgery. Low initial subjective score and inability to abduct the arm at presentation were risk factors for a poor outcome

The aim of this study was to determine the effect of a Galeazzi fracture on the strength of pronation and supination at a mean of two years after surgical treatment. The strength of pronation and supination was measured in varying rotational positions of the forearm of ten male patients (mean age 38.9 years (21 to 64)) who had undergone plate fixation for a Galeazzi fracture. The stability of the distal radioulnar joint was assessed, and a clinical assessment using the quick-Disabilities of the Arm Shoulder and Hand (quickDASH) questionnaire and patient-related wrist examination (PRWE) scores was undertaken. In addition, the strength of pronation and supination was measured in a male control group of 42 healthy volunteers (mean age 21.8 years (18 to 37)).

The mean absolute loss of strength of supination in the injured compared with the non-injured arm throughout all ranges of forearm rotation was 16.1 kg (sem 5.3), corresponding to a relative loss of 12.5% (95% confidence interval (CI) 3.6 to 21.4). For the strength of pronation, the mean loss was 19.1 kg (sem 4.5), corresponding to a relative loss of 27.2% (95% CI 14.2 to 40.1). Loss of strength of supination following a Galeazzi fracture correlated with poor quickDASH (p = 0.03) and PRWE scores (p < 0.01).

Loss of strength of pronation (27.2%), and of supination (12.5%) in particular, after a Galeazzi fracture is associated with worse clinical scores, highlighting the importance of supination of the forearm in function of the upper limb.

Cite this article: Bone Joint J 2013;95-B:1508–13.

Introduction. Total leg muscle function in hip OA patients is not well studied. We used a test-retest protocol to evaluate the reproducibility of single- and multi-joint peak muscle torque and rapid torque development in a group of 40–65 yr old hip patients. Both peak torque and torque development are outcome measures associated with functional performance during activities of daily living. Material and Methods. Patients: Twenty patients (age 55.5±3.3, BMI 27.6±4.8) who underwent total hip arthroplasty participated in this study. Reliability: We used the intra-class correlation (ICC) and within subject coefficients of variation (CVws) to evaluate reliability. Agreement: Relative Bland-Altman 95% limits of agreements (LOA) and smallest detectable difference (SDD) were calculated and used for evaluation of measurement accuracy. Parameters: Maximal muscle strength (peak torque, Nm) and rate of torque development (Nm•sec-1) for affected (AF) and non-affected (NA) side were measured during unilateral knee extension-flexion (seated), hip extension-flexion, and hip adduction-abduction (standing), respectively. Contractile RTD100, 200, peak was derived as the average slope of the torque-time curve (torque/time) at 0–100, 0–200 and 0 peak relative to onset of contraction. Protocol: After 5 min level walking at self-selected and maximum speeds each muscle group was tested using 1–2 sub-maximal contraction efforts followed by 3 maximal contractions 4s duration. Statistics: The variance components were estimated using STATA12, with muscle function and occasion as independent variable and patients as random factor, using the restricted maximum likelihood method (=0.05). Results. For all exercises and sides, the ICC's for peak torque were good (0.81–0.96) with CVws ranging from 5.0–10.8%. Similar good ICC's were observed for RTD200 on the non-affected side (0.83–0.93), whereas most exercises (4/6) on the affected side showed moderate to good ICC (0.72–0.82). We found moderate CVws for RTD200 with 12.8–18.7% and 10.3–18.9%, affected and non-affected, respectively. With few exceptions the ICC's and CVws for RTD100 were moderate to poor on the affected side but good to moderate on the non-affected side. The SDD's for peak torque ranged from 14.9 Nm to 39.0 Nm, equal to relative LOA of 13.9–23.8%. For RTD200, the SDD's were 77–257 Nm•sec-1 and 29.2–86.2%, absolute and relative, respectively. With few exceptions interventions measuring RTD100 and RTDpeak would have to find changes exceeding 60% for them to be statistical significant. Conclusions. Our novel set-up for lower limb isometric muscle testing showed overall good reproducibility for peak torque, moderate for RTD200, while poor for RTD100 and RTDpeak. The results for peak torque and RTD200 are promising for defining relevant changes in muscle function in future longitudinal clinical trials in this patient group

Purpose: The reverse total shoulder arthroplasty (RTSA) has shown improvement in both pain control and function in recent studies. The purpose of this study was to prospectively analyze functional outcomes and strength in patients following the use of the Delta III prosthesis in a single center. Method: Patients treated by one of two surgeons were prospectively evaluated following RTSA. An independent observer administered the Constant Score, SF-12, Shoulder Osteoarthritis (SOAQ), ASES, DASH questionnaires and patient satisfaction. Isometric strength testing was performed using the Powertrack II dynamometer. Follow-up for all patients was available up to 5 years following surgery. Results: The Delta III RTSA was performed on 51 study patients (67% female, mean age 74 (SD=10)). Improvements following surgery were noted in Quality of life (SF-12 Physical Summary= 30 to 38); shoulder disability (SOAQ= 144 to 79; ASES 7 to 15; DASH= 61 to 46; Constant 21 to 56), Symptoms (SOAQ symptoms 40 to 22), Physical impairments as determined by strength (External rotation = 3 to 5 Nm, Abduction 4 to 10 Nm); and ROM (Flexion= 51 to 115°, abduction 45 to 106°); p< 0.05. All patients had follow up between 2–5 years. Satisfaction was high (86% extremely, 3% not at all). Conclusion: Our data demonstrates significant improvements in quality of life, symptoms, patient satisfaction and disability with reduced and high at more than 2 years following RTSA. Novel to this study is improved objective evidence of strength in functional planes of motion. This is the first Canadian study to demonstrate such improvements in patients following RTSA

Purpose: Open reduction internal fixation with a volar plate is a popular surgical option for distal radius fractures. The pronator quadratus (PQ) must be stripped from the distal radius in this procedure. PQ is an important pronator of the forearm and stabilizer of the distal radioulnar joint. The purpose of this study was to investigate pronation torque in healthy volunteers before and after temporary paralysis of the PQ with lidocaine under EMG guidance. Method: A custom-made apparatus was built to allow isometric testing of pronation torque at 5 positions of rotation: 90° of supination, 45° of supination, neutral, 45° of pronation and 80° of pronation. It was validated using a test-retest design with 10 subjects. For the study, 17 (9 male, 8 female) right hand dominant volunteers were recruited. They were tested at all 5 positions in random order and then had their PQs paralyzed with lidocaine. Repeat testing was performed in the same random order 30 minutes after injection. Three subjects underwent unblinded testing with saline injected instead of lidocaine. Results: After paralysis of PQ with lidocaine, pronation torque decreased by 23.2% (p=0.0010) at 90° of supination, 16.7% (p=0.0001) at 45° of supination, 22.9% (p=0.0002) in the neutral position, 20.4% (p=0.0066) at 45° of pronation and 22.2% (p=0.0754) at 80° of pronation. All were statistically significant except 80° of pronation. Peak torque values before and after injection were highest in the supinated positions (8.2 Nm at 45° supination) and decreased gradually as the subjects were in more pronated positions (1.8 Nm at 80° pronation). The test-retest trial demonstrated no evidence of fatigue with repeated testing. The subjects who underwent injection of saline demonstrated no evidence of pronation torque loss secondary to pain or a pressure effect of the injectate. Conclusion: This study demonstrated a significant decrease in pronation torque with controlled elimination of PQ function. Open reduction internal fixation of distal radius fractures damages the PQ. This may result in a pronation torque deficit. Functional significance of this loss should be shown. Pronation torque measurement may add to postoperative outcome analysis of surgical procedures about the wrist

Between 1995 and 2006, five intra-articular osteotomies of the head of the radius were performed in patients with symptomatic healed displaced articular fractures. Pre-operatively, all patients complained of persistent painful clicking on movement. Only patients with mild or no degenerative changes of the radial head and capitellum were considered for osteotomy. The operations were performed at a mean of 8.2 months (4 to 13) after injury and the patients were reviewed at a mean of 5.5 years (15 months to 12 years) after the osteotomy.

The average Mayo Elbow Performance Index Score improved significantly from 74 before to 88 after operation, with four patients rated as good or excellent (p < 0.05). The subjective patient satisfaction score was 8.4 on a ten-point scale. All osteotomies healed and there were no complications.

In this small series intra-articular osteotomy of the head of the radius was a safe and effective treatment for symptomatic intra-articular malunion without advanced degenerative changes.

Sprains and strains result from collagen fibre overextension. This study investigated changes in the molecular state of collagen due to overextension damage, thereby gaining insight into tissue degeneration and cellular detection of damage. Overextension results in intermolecular and intrafibrillar sliding, detected with x-ray diffraction. Tendon rupture results in increased susceptibility to proteolytic enzymes. These observations and contemporary theory concerning collagen fibre stability lead to the hypothesis that sub-rupture overextension should result in reduced thermal stability of fibrous collagen. Tendons were harvested from steer tails. Each provided a specimen for control and for overextension. Sub-rupture overextension at 1%/s strain rate was accomplished on a mechanical testing system, under the control of custom software, until the slope of the force-deformation curve was approximately zero (before complete failure). Two loading treatments were tested: one-cycle and five-cycles. Two specimen types were tested: native tendons ± NaBH4 crosslink stabilization. Tendons in each of the four groups (2x2) were paired by originating tail. Thermal stability was assessed in terms of denaturation temperature (Td) using hydrothermal isometric tension testing. Specimens were held at constant length and heated from ambient temperature to 90degC. Td was defined as the temperature where load suddenly increased due to molecular unraveling and attempted shrinkage. Overextension of native specimens reduced the thermal stability of the collagen (p< 0.0001) and five-cycles had a still greater effect (p=0.03). Td of controls was 64.5±1.0degC (mean±SD). After one-cycle, Td dropped to 63.2±1.0degC and, after five-cycles, Td dropped to 61.8±2.0degC. For stabilised tendons, the effect of multiple cycles was lost (p=0.08) but overstretching decreased Td by ~2degC (p< 0.0001). This study confirms that the molecular state of collagen is altered by overextension damage, reducing Td by up to 10% of the expected range (37–65degC) in our experiments. This is thought to occur due to intermolecular sliding that liberates specific domains on the molecules, lowering the activation energy for uncoiling. These domains may also be key targets in degeneration and cell-collagen signaling

We present the operative technique and clinical results of concomitant reconstruction of the medial collateral ligament (MCL) and the posterior oblique ligament for medial instability of the knee using autogenous semitendinosus tendon with preservation of the tibial attachment. The semitendinosus tendon graft between the screw on the medial epicondyle and the tibial attachment of the graft was overlapped by the MCL, while the graft between the screw and the insertion of the direct head of the semimembranosus tendon was overlapped by the central arm of the posterior oblique ligament. Assessment was by stress radiograph and the Lysholm knee scoring scale. After a mean follow-up of 52.6 months (25 to 92), the medial joint opening of the knee was within 2 mm in 22 of 24 patients. The mean Lysholm score was 91.9 (80 to 100).

Concomitant reconstruction of the MCL and posterior oblique ligament using autogenous semitendinosus tendon provides a good solution to medial instability.

Rowing is associated with a high incidence of low back pain (LBP) often attributed to the associated loading and large trunk rotations. Here we examine electromyographic (EMG) activity in rowers who undertake sweep rowing (asymmetrical) or sculling (symmetrical). 22 right handed elite rowers participated and written informed consent was obtained. Each had a preferred rowing side (bow side [BS, n=6]; stroke side [SS, n=7) or sculling [SC, n=9]). Testing was performed in a Cybex isokinetic dynamometer and bilateral EMG activity recorded from trunk muscles (erector spinae [ES] and rectus abdominis [RA]) synchronously. There were no differences between the groups in peak torque during isokinetic or isometric testing, although extensor torque was higher than flexor torque. Analysis of EMG activity revealed that scullers showed no left/right differences in any of the testing protocols. However, sweep rowers showed significant differences between left and right ES during extension protocols, in the isokinetic testing at 30°s. −1. (in the SS rowers [LES 0.11±0.01mV vs RES 0.08±0.01mV] and at 90°s. −1. in the BS rowers [LES 0.14±0.02mV vs RES 0.12±0.01mV]. In the isometric tests, the SS rowers showed higher left ES activity than the right [LES 0.11±0.01mV vs RES 0.09±0.01mV]. The flexion protocols did not reveal any left right differences in any groups in any of the protocols used. These results reveal that sweep rowing is associated with asymmetric activity of trunk extensors, but not flexors. This could be a contributing factor to the high incidence of LBP in sweep rowers

Trunk flexor-extensor asymmetry has been implicated in the development of back pain; however, left-right trunk muscle asymmetry has received little attention. This study examined whether such left-right asymmetries exist and if these are related to differing sporting tasks. Thirty-five subjects were recruited and written informed consent obtained; 12 subjects participated in unilateral (UL) sports e.g. racquet sports (mean age 21.6±0.7 (SEM) years), 13 in bilateral (BL) activities e.g. rugby (mean age 21.7±0.2) and 10 controls (C) not involved in sport (mean age 21.7±0.2) years). Isokinetic and isometric trunk flexions and extensions including a fatiguing isometric hold were performed in a Cybex isokinetic dynamometer synchronised with bilateral electromyographic (EMG) recordings from trunk extensors (erector spinae at L4), and flexors (rectus abdominis at T10). A ratio of left:right EMG activity was calculated for each set of muscles, to examine asymmetry. No differences were seen in left:right extensor EMG ratios across any of the test protocols. However, the UL group had higher (P< 0.05) left:right flexor EMG ratios than the BL group during pre-fatigue (UL:1.32±0.15 vs. BL:0.84±0.07) and post-fatigue (UL:1.30±0.18 vs BL:0.84±0.07) isometric flexion. Torque data suggested that the trunk extensor-flexor ratio was larger (P< 0.05) in the BL group compared to the C in the isokinetic exercises at the 30°s. −1. (BL:1.27±0.05; C:1.00±0.06) and at the 90°s. −1. speeds (BL:1.28±0.05; C:0.95±0.08), but no differences were seen during isometric testing. This study suggests that training for different sports can generate significant asymmetry in the trunk muscles, particularly in the flexors, the importance of which requires further research

This study prospectively evaluated the functional outcome and strength of patients after rotator cuff surgery. Thirty-three patients were evaluated pre-operatively and post-operatively for one year. Each patient underwent clinical evaluation of shoulder range of motion and machine strength testing. Additionally they completed the SF-36, DASH, Western Ontario Rotator Cuff, and Washington Simple Shoulder Test questionnaires. The study showed that patients with small and large tears showed improvement after surgery. Smaller tears had better outcomes. Workplace Safety and Insurance Board (WSIB) patients had lower functional outcomes despite strength and range of motion showing no difference with non- WSIB patients. This study prospectively evaluated strength and functional outcome after rotator cuff surgery. Thirty-three patients, mean age 55.6, were evaluated pre-operatively and post-operatively for one year. Twenty-eight patients were male and five were female. Seventeen patients involved the Workplace Safety and Insurance Board and sixteen patients had non-WSIB related tears. The patients were also divided based on tear size into two groups (< 3cm and > 3.1cm). Allpatients underwent an acromioplasty. Twenty-two also had an open or mini-open repair. Two underwent arthroscopic repair. Five patients had a debridement and four patients had Latissimus Dorsi Transfer. All had an evaluation of range of motion(ROM), machine isometric strength testing, and completion of the SF-36, DASH, Western Ontario Rotator Cuff (WORC) and Washington Simple Shoulder Test (WST) at each visit. Based on tear size, there was a significant difference in functional outcome on the SF-36 (p< 0.05), DASH (p< 0. 005), WORC (p< 0.001) and WST (p< 0.01). Within each group there was significant improvement in strength (p< 0.01) over time. The smaller tear group showed significantly greater strength. The ROM was improved within each group over time (p< 0.01), though no statistical difference was determined between groups. In comparing the sample based on WSIB status, functional outcomes were better in Non-WSIB patients (p< 0.01). Although no statistical difference in strength and ROM was noted. Patients with both small and large tears showed improved functional outcome, strength and ROM over time, with the smaller tear group having better outcomes. WSIB patients had lower functional outcomes despite strength and ROM showing no difference between the two groups

We undertook a multicentre, prospective study of a series of 112 unstable trochanteric fractures in order to evaluate if internal fixation with a sliding screw device combined with augmentation using a calcium phosphate degradable cement (Norian SRS) could improve the clinical, functional and radiological outcome when compared with fractures treated with a sliding screw device alone. Pain, activities of daily living, health status (SF-36), the strength of the hip abductor muscles and radiological outcome were analysed.

Six weeks after surgery, the patients in the augmented group had significantly lower global and functional pain scores (p < 0.003), less pain after walking 50 feet (p < 0.01), and a better return to the activities of daily living (p < 0.05). At follow-up at six weeks and six months, those in the augmented group showed a significant improvement compared with the control group in the SF-36 score. No other significant differences were found between the groups. We conclude that augmentation with calcium phosphate cement in unstable trochanteric fractures provides a modest reduction in pain and a slight improvement in the quality of life during the course of healing when compared with conventional fixation with a sliding screw device alone.

Background: Prospective population studies demonstrate that poor paraspinal muscle endurance increases the risk of developing first-time LBP and many CLBP studies also document excessive paraspinal muscle fatigability. The question arises as to whether this could have predisposed to chronic symptoms, through impaired spinal instability, especially in light of the wide inter-individual variation observed in the constitutionally determined paraspinal muscle fibre-type composition, which governs contractile performance. Objective: To determine whether CLBP-associated excessive paraspinal fatigue results from a paucity in the type I fibre content. Design: Control comparison using male subjects. Subjects: Thirty-five CLBP patients with Von-Korff Chronic Pain Scores of ≤ III (high level of residual function, despite pain, to negate effects of disuse atrophy), and 32 controls of similar age. Outcome measures: Fatigue-induced median frequency (MF) declines in the surface EMG signal, monitored bilaterally at L4 level during Biering-Sorensen- and 60%MVC- isometric fatigue tests. Percutaneous para-spinal muscle biopsies permitted histomorphometric comparisons. Results: Between-group differences were assessed using independent t-tests (p < 0.05). There were no differences for MF decline during the Biering-Sorensen -0.37(0.16) vs. -0.36(0.12), and the 60% MVC test −0.42(0.31) vs −0.51(0.29), and in the percentage number of type I fibres, 63.6% vs 64.3%, or percentage area occupied by type I fibres, 69.4% vs 67.2%, in the paraspinal muscles for patients and controls respectively (p> 0.05). Conclusion: Impaired CLBP-associated endurance is not the result of a constitutionally ‘adverse’ fibre-type composition

Paraspinal muscle dysfunction is associated with chronic low back pain (CLBP) in prospective studies, some authors suggesting a primary role for muscle in CLBP development. To investigate this possibility, we compared paraspinal muscle electromyographic (EMG) fatigue characteristics with fibre-type composition in ambulant, male CLBP patients and male controls of similar age. Thirty-five patients with Chronic Pain Grades of III (a high level of residual function, despite pain, negated the effects of disuse atrophy), and 32 controls were studied. Paraspinal surface EMG signals were recorded from the T10/11 and L4/5 regions bilaterally during standard isometric endurance tests. The rate of fatigue-induced median frequency (MF) decline was calculated from the power spectrum. Percutaneous paraspinal muscle biopsies permitted the determination of muscle fibre-type characteristics. MF decline, mean fibre size and relative area occupied by fibre types did not differ significantly between groups. The paraspinal muscles of ambulant CLBP patients demonstrate no excessive fatigability, when assessed by EMG, nor a relative paucity in the area occupied by either fibre type. Patients developing CLBP do not demonstrate an adverse paraspinal muscle fibre-type composition