Ibuprofen vs. acetaminophen vs. ibuprofen and acetaminophen after arthroscopically assisted anterior cruciate ligament reconstruction.

BACKGROUND AND OBJECTIVE: The analgesic potency of non-steroidal anti-inflammatory drugs and acetaminophen are still being debated. We have assessed the relative analgesic effect of ibuprofen, acetaminophen or the combination of both after orthopaedic surgery. METHODS: Sixty-one ASA I patients, scheduled for an elective anterior cruciate ligament reconstruction under general anaesthesia were randomized, in a double blind fashion, into one of three groups. The ibuprofen group (n = 17) received ibuprofen 800 mg orally 1 h before operation and again at 6 and 12 h after the initial dose. The acetaminophen group (n = 20) received of acetaminophen 1 g orally at the same time intervals. The combination group (n = 24) received both ibuprofen 800 mg and acetaminophen 1 g. Surgery was performed under general anaesthesia with propofol and fentanyl for induction and maintenance with propofol and nitrous oxide in oxygen. The patients were monitored for 24 h thereafter, and the following variables were assessed: pain by visual analogue and verbal scales, need for rescue intravenous opioid analgesia (i.e. ketobemidone) and adverse events. RESULTS: The ibuprofen group and the combination group experienced significantly less pain during the first 6 h after surgery than the acetaminophen group using the visual analogue and the verbal scales. The acetaminophen group also had a significantly higher average consumption of opioids during the first 6 and 24 h. There were no significant differences between the ibuprofen group and the combination group in respect of experienced pain or consumption of rescue analgesia. The incidence of side-effects, postoperative haemoglobin concentration and renal function, judged by creatinine clearance, were identical between the groups. CONCLUSION: Ibuprofen 800 mg thrice daily reduced pain to a greater degree than acetaminophen 1 g thrice daily, after anterior cruciate ligament reconstruction under general anaesthesia. The combination of acetaminophen and ibuprofen did not provide any superior analgesic effect.

Subjective functional assessments and the return to competitive sport after anterior cruciate ligament reconstruction.

OBJECTIVES: To examine (a) return to competitive sport within 12 months of anterior cruciate ligament (ACL) reconstruction, (b) maintenance of competitive participation at follow up, and (c) the relation of the level of sports activity and competitive participation at follow up to subjective functional assessments. Also to address the incidence of continued competitive participation despite notable functional problems with the operated knee at 12 months and follow up. METHODS: All patients were competitive athletes before injury and had undergone ACL reconstruction by the transtibial endoscopic technique with either a bone-patellar tendon-bone or a multiple looped hamstring autograft. Evaluation was carried out a mean of 43 months (range 24-73) after surgery by a postal questionnaire in which the Cincinnati sports activity scale (CSAS) and Cincinnati sports function scales were presented in conjunction with closed questions on change in competitive level and the presence of complaints. RESULTS: Of 109 selected patients, 77 (71%) responded. At follow up, 62 of 77 patients (81%) reported that they had returned to competition within 12 months of surgery. Within the same time frame, 55 of the above 62 patients (89%) also claimed to have returned to the level at which they were competing before injury (or higher). At follow up, 30 of the above 55 patients (54%) reported to still be competing at this high level. Twelve of the above 55 patients (22%) also admitted to major problems with the operated knee at that time. The overall incidence of patients competing despite major functional impairment in the operated knee was 13 of 62 (21%) at 12 months and six of 47 (13%) at follow up. Thirty eight patients (49%) were active in sport at least four times a week at follow up (CSAS level 1), and, using Spearman's rank correlation between CSAS scores and total sports function scores, r was calculated to be 0.44. Competitive and male patients had higher total sports function scores at follow up than non-competitive (p = 0.005) and female (p = 0.02) patients respectively. CONCLUSIONS: The reported return to competition at the previous level, both within 12 months and at follow up, was high but as expected considering the standard of treatment, patient selection, and study exclusion criteria. Patients with few functional complaints maintained a high level of sporting activity, even after discontinuing competitive participation.

Four-strand hamstring tendon autograft compared with patellar tendon-bone autograft for anterior cruciate ligament reconstruction. A randomized study with two-year follow-up.

Seventy-two patients with subacute or chronic rupture of the anterior cruciate ligament were randomly assigned to autograft reconstruction with four-strand gracilis and semitendinosus tendon (N = 37) or with patellar tendon-bone (N = 35) from the ipsilateral side. The groups were similar in terms of age, sex, level of activity, degree of laxity, meniscal lesions found surgically, and rehabilitation program. The follow-up was performed at another hospital by independent observers after 6, 12, and 24 months. Sixty-one patients (32 with hamstring tendon grafts and 29 with patellar tendon grafts) complied with the follow-up routine for the full 24 months. No differences were found between the groups with respect to Cincinnati functional score, KT-1000 arthrometer measurements, or stairs hopple test results. The subjective result and the single-legged hop test result were better for the hamstring tendon group after 6 and 12 months, but no differences were found after 24 months. The hamstring tendon group showed better isokinetic knee extension strength than did the patellar tendon group after 6 months, but not after 12 and 24 months. There was a significant weakness in isokinetic knee flexion strength among the hamstring tendon group. Anterior knee pain was not significantly different between the groups, but kneeling pain was significantly less common in the hamstring tendon group after 24 months.

Traditional Chinese medicine syndromes in women with frequently recurring cystitis: frequencies of syndromes and symptoms.

BACKGROUND: Frequently recurrent acute cystitis in adult women is common in Western medicine. In prophylactic treatment, women are treated between attacks of acute cystitis to prevent recurrences. A recent study has shown that acupuncture seems effective for prophylaxis. OBJECTIVES: To describe the frequency of traditional Chinese medicine (TCM) syndromes found in females vulnerable to recurrent cystitis, and which symptoms most often form the basis for TCM diagnoses made in this condition. METHODS: A descriptive study based on TCM diagnostic methods as used by experienced acupuncturists, and a questionnaire of symptoms used in TCM diagnostics. RESULTS: Of 61 women with frequently recurring cystitis, 90% were diagnosed as having either a Spleen/Kidney yang xu/qi xu (54%), or a Liver qi stagnation (36%). Only 10% fell in other diagnostic groups. Of all symptoms noted, only three differed in frequency between the two main diagnostic groups: feeling cold (29/33 vs. 13/22, P<0.05), feeling tired (25/33 vs. 4/22, P<0.001), and having a preference for sweets (10/33 vs. 2/22, P<0.05). CONCLUSION: Our findings have implications for TCM-based diagnostic work in females with recurrent cystitis, and also indicate that recurrent cystitis may be used as a case for further TCM research.

[Treatment of knee osteoarthritis]. / Behandling av kneleddsartrose.

Osteoarthritis of the knee is not a well defined illness, but is a result of different causes that may lead to joint failure due to chondral damage, synovial inflammation, subchondral bone formation, and the formation of osteophytes along the joint lines. The pathogenesis is unclear. We still lack treatment to cure the early process of chondral degeneration. The treatment of choice in early and moderate osteoarthritis of the knee is limited to counselling, physiotherapy, analgesics, and surgical correction of malalignment. Documentation is still lacking on chondral debridement and transplantation of the degenerated cartilage by cultured chondrocytes, periosteum or perichondrium. An effective and well documented treatment of end-stage osteoarthritis of the knee in the older population is replacement of the joint by a knee prosthesis.

Fracture healing and callus innervation after peripheral nerve resection in rats.

The effects of femoral and sciatic nerve resection on fracture healing and innervation of the fracture callus were studied using a stable fracture model. In 34 rats the right tibia was subjected to a standardized closed fracture and stabilized with a modular intramedullary nail. In half of the animals, resection of 1 cm of the femoral and sciatic nerves was performed (nerve resection group), whereas the other animals had sham operations (sham group). To avoid unequal load-bearing between the two groups, all fractured hindlimbs were immobilized in a plaster of Paris cast. The trial was terminated after 5 weeks of fracture healing. Callus size was scored radiographically, and bone mineralization was measured by 85-strontium incorporation. Seven rats from each group had immunohistochemical examination for neural regeneration and ingrowth. Antisera for protein gene product 9.5, neurofilaments, neural growth associated protein 43/B-50, calcitonin gene related peptide, and substance P were used. The mechanical properties of the healing fractures were recorded in a three-point cantilever bending test. After 5 weeks, the normally innervated, fractured tibias had regained approximately 50% strength compared with the unfractured side, in comparison with only 20% in the animals that had nerve resection. Although the fracture calluses were mechanically weaker, they were significantly larger in the nerve resection group, indicating defects in tissue composition or organization rendered by the nerve injury. The mineralization rate, as measured by 85-strontium incorporation, was the same in the two groups. However, the nerve resection did not provide complete denervation but changed the innervation pattern of the healing fracture, as the density of sensory nerve fibers immunostaining for substance P and neurofilaments was less in the group with femoral and sciatic nerve resection. The results suggest that intact innervation is essential for normal fracture healing because nerve injury induced a large, but mechanically insufficient, fracture callus.

Acupuncture in the prophylaxis of recurrent lower urinary tract infection in adult women.

OBJECTIVE: To evaluate the effect of acupuncture in the prevention of recurrent lower urinary tract infection (UTI) in adult women. DESIGN: A controlled clinical trial with three arms: an acupuncture group, a sham-acupuncture group, and an untreated control group. Patients were followed for 6 months. SETTING: An acupuncture clinic in Bergen, Norway. SUBJECTS: Sixty-seven adult women with a history of recurrent lower UTI. MAIN OUTCOME MEASURES: Acute lower UTIs during the 6-month observation period. RESULTS: Eighty-five percent were free of lower UTI during the 6-month observation period in the acupuncture group, compared with 58% in the sham group (p < 0.05), and 36% in the control group (p < 0.01). There were half as many episodes of lower UTI per person-half-year in the acupuncture group as in the sham group, and a third as many as in the control group (p < 0.05). CONCLUSION: Acupuncture seems a worthwhile alternative in the prevention of recurring lower UTI in women.

Dynamic hip screw with trochanteric stabilizing plate in the treatment of unstable proximal femoral fractures: a comparative study with the Gamma nail and compression hip screw.

OBJECTIVE: To compare the results after operative treatment of unstable per- and subtrochanteric fractures with the Gamma nail, compression hip screw (CHS), or dynamic hip screw with a laterally mounted trochanteric stabilizing plate (DHS/TSP). DESIGN: Prospective. PATIENTS: One hundred seventy patients with unstable trochanteric femoral fractures surviving six months after operation. Eighty-five patients were randomized to treatment with the Gamma nail (n = 50, Gamma group) or the compression hip screw (n = 35, CHS group) and compared with a consecutive series of eighty-five patients operated with the dynamic hip screw with a laterally mounted trochanteric stabilizing plate (DHS/TSP group) MAIN OUTCOME MEASUREMENTS: Radiographs were analyzed for fracture classification, evaluation of fracture reduction, implant positioning, later fracture dislocation, and other complications. Pre- and postoperative functional status of the patients were recorded, with a minimum of six months follow-up. RESULTS: Eighteen percent of the patients in the Gamma group, 34 percent in the CHS group, and 9 percent in the DHS/TSP group suffered significant secondary fracture dislocation during the six months follow-up, leading to a varus malunion, lag screw cutout, or excessive lag screw sliding with medialization of the distal fracture fragment. Two patients (4.0 percent) in the Gamma group suffered an implant-related femoral fracture below the nail, and one had a deep infection. The reoperation rates were 8.0 percent in the Gamma group, 2.9 percent in the CHS group, and 5.9 percent in the DHS/TSP group. All but one fracture in the Gamma and CHS groups and two fractures in the DHS/TSP group healed within six months. Approximately three-fourths of the patients had returned to their preoperative walking ability after six months, with a trend toward better functional outcome in the DHS/TSP group. Use of a TSP reduced the secondary lag screw sliding as compared with the conventional CHS, without affecting fracture healing. CONCLUSION: The TSP may be an aid in the treatment of these difficult fractures because the problem with femoral shaft fractures using the Gamma nail is avoided and the medialization of the distal fracture fragment frequently associated with the CHS is prevented.

Interference screw fixation of hamstring vs patellar tendon grafts for anterior cruciate ligament reconstruction.

The present study was designed to investigate the fixation strength of a quadruple semitendinosus-gracilis graft compared with a middle-third bone-patellar tendon-bone graft using a new interference screw developed to fix hamstrings grafts for ACL reconstructions (RCL Smith & Nephew Donjoy). Five pairs of human cadaveric knees from donors with a mean age of 43 (range 33-52) years were used. One knee of each pair was randomly allocated to be reconstructed on the femoral side with a semitendinosus-gracilis graft from the same donor using RCL screw fixation. As the control, the contralateral knee was correspondingly reconstructed with a bone-patellar tendon-bone graft using the same interference screw. The grafts were pulled out at a velocity of 30 mm/s by an axially applied load using a MTS machine. The mean (SD) failure load for the bone-patellar tendon-bone graft fixations was 505 (25) N, 110% stronger than the mean failure load for the semitendinosus-gracilis graft fixations, which was 240 (47) N (P = 0.003). The stiffness for the patellar tendon-bone graft fixations was 46 (11) N/mm, 120% stiffer than the semitendinosus-gracilis graft fixations, which was 22 (11) N/mm (P = 0.01). This study shows that the interference screw principle used for ACL reconstructions with hamstrings tendons is inferior to that for bone-patellar tendon-bone reconstructions although the screw was developed especially for soft-tissue fixation in bone tunnels.

[Can acupuncture prevent cystitis in women?]. / Kan akupunktur forebygge blaerekatarr hos kvinner?

67 adult women with a history of recurrent lower urinary tract infection (UTI) were randomized for acupuncture treatment, sham acupuncture, or no treatment. The incidence rate of UTI over the following six months was noted. In the acupuncture group a total of 85% was free of cystitis during the six-month observational period, as compared to 58% in the sham group (p < 0.05), and 36% in the control group (p < 0.01). Compared to the acupuncture group, twice as many incidents of cytitis occurred in the sham group, and three times as many in the control group (p < 0.05). Acupuncture seems a worthwhile alternative in the prevention of frequently recurring cystitis in women.

Anterior cruciate ligament strength. Can it be estimated by non-destructive testing?

For structural and material bone strength, non-destructive tests exist, while no such tests have been developed for ligaments. In the present study we compared the geometry and bone mineral content (BMC) of the rat tibia with the tensile strength of the anterior cruciate ligament (ACL). A significant correlation was found between the mediolateral diameter of the tibial condyle and ACL load to failure (r=0.83). Calculating the area of the condyle as an ellipse increased this correlation to r=0.93. No significant correlation was found to BMC. If this correlation is also found in humans, the mediolateral tibial head diameter may be used to estimate the strength of the ACL non-destructively.

Quadriceps muscle contraction protects the anterior cruciate ligament during anterior tibial translation.

The proposed skiing injury mechanism that suggests a quadriceps muscle contraction can contribute to anterior cruciate ligament rupture was biomechanically investigated. The effect of quadriceps muscle force on a knee specimen loaded to anterior cruciate ligament failure during anterior tibial translation was studied in a human cadaveric model. In both knees from six donors, average age 41 years (range, 31 to 65), the joint capsule and ligaments, except the anterior cruciate ligament, were cut. The quadriceps tendon, patella, patellar tendon, and menisci were left intact. One knee from each pair was randomly selected to undergo destructive testing of the anterior cruciate ligament by anterior tibial translation at a displacement rate of 30 mm/sec with a simultaneously applied 889 N quadriceps muscle force. The knee flexion during testing was 30 degrees. As a control, the contralateral knee was loaded correspondingly, but only 5 N of quadriceps muscle force was applied. The ultimate load for the knee to anterior cruciate ligament failure when tested with 889 N quadriceps muscle force was 22% +/- 18% higher than that of knees tested with 5 N of force. The linear stiffness increased by 43% +/- 30%. These results did not support the speculation that a quadriceps muscle contraction contributes to anterior cruciate ligament failure. In this model, the quadriceps muscle force protected the anterior cruciate ligament from injury during anterior tibial translation.

Completion rates and injuries in alpine races during the 1994 Olympic Winter Games.

The starting lists for the alpine disciplines during the 1994 Olympic Winter Games in Lillehammer totalled 555 racers, but only 354 of them (64%) completed the different races. The race completion rate was 43% in the slalom, 51% in the giant slalom, 75% in the super giant slalom and 91% in the downhill. In combined downhill/slalom the race completion rate was 60%, but 96% in the downhill and 68% in the slalom part of the combination, respectively. Only three injuries were recorded, all in females. Including the training competitions a total of 1541 runs through the different alpine courses was recorded during the games. This means an injury rate of 1.9 injuries per 1000 runs. For downhill the injury rate was only 1.1 per 1000 runs. If the injury rate is related to the number of skiers who did not finish the race because of falls or skiing errors, the rate was 21.1 injuries per 1000 falls (skiing errors) for all alpine races. In conclusion, the race completion rate was twice as high in downhill as in slalom, and the injury rate was low.

Structural capacity of the knee to anterior cruciate ligament failure during quadriceps contraction. An in vivo study in the rat.

The effect of quadriceps contraction on the structural capacity of the knee joint loaded to anterior cruciate ligament (ACL) failure was studied in an in vivo rat model. In both knees of 20 rats the joint capsule and ligaments, except the ACL, were cut and the menisci resected by microsurgery. The rats were randomized to destructive testing of their ACLs either by femorotibial distraction or by anterior tibial translation at a displacement rate of 2.5 mm s-1 (60% s-1). The knee flexion during testing was 60 degrees. During loading of the right ACL, quadriceps contraction was induced by electrical stimulation of the femoral nerve. As control, the ACL of the left knee was loaded with relaxed quadriceps. The ultimate load for the knee to ACL failure when tested in tension by femorotibial distraction during quadriceps contraction was 140% higher than tested with the muscles relaxed (p = 0.0001). Energy absorption at failure during muscle contraction was 274% higher (p = 0.0001), and the linear stiffness increased by 59% (p = 0.0004). During testing by anterior tibial translation, neither linear stiffness nor ultimate load changed significantly, but the energy absorbed at failure was 46% (p = 0.02) higher during quadriceps contraction compared to testing with the quadriceps relaxed. These results showed that quadriceps contraction substantially increased the load carrying capacity of the rat knee subject to ACL failure when loaded by femorotibial distraction, but less when it was loaded by anterior tibial translation.

Neural involvement in post-traumatic osteopenia: an experimental study in the rat.

The effect of sciatic nerve resection on post-traumatic bone loss and mechanical strength of the ipsilateral (IL) and contralateral (CL) femoral shafts and necks was studied 25 days after a tibial fracture. We subjected 45 male rats to a standardized tibial fracture, stabilized it with a modular intramedullary nail and then randomly allocated the animals to two groups: right sciatic nerve resection (SNR group) or sham operation (sham group). All of the operated hindlimbs were further immobilized in a plaster cast to avoid unequal loadbearing between the two groups. After 25 days of healing, 85Sr incorporation in the IL femora was 10% lower in the SNR group compared to the sham group, indicating a lower bone mineralization after sciatic nerve resection. The bone mineral content was 15% higher in the SNR group ipsilaterally. Accordingly, the bending moment and energy absorption in the femoral midshaft were higher in the SNR group compared to the sham group. The sciatic nerve resection protected the femoral shaft against the normally occurring post-traumatic bone loss after a tibial fracture. This protective effect of the neurectomy also occurred in the femoral neck, but not to the same extent. A protective effect was also present in the CL femur, suggesting additional systemic effects of the sciatic nerve resection.

Comparison of failure strength between metallic and absorbable interference screws. Influence of insertion torque, tunnel-bone block gap, bone mineral density, and interference.

Because of the good initial fixation strength of interference screws used in anterior cruciate ligament reconstruction, metal interference screws have become the standard method for fixation of bone-patellar tendon-bone grafts. To avoid some of the complications with metal screws, a bioabsorbable interference screw was developed. Data on fixation strength in older human cadavers indicate a similar failure strength between bioabsorbable and metal screws. We studied the failure mechanisms, insertion torques, and fixation strengths of absorbable and metal interference screws in cadaveric knees from young and middle-aged donors. With identical gap and screw size, the mean insertion torque for the metal screws (mean, 1.5 N-m; SD, 0.8) was significantly higher than for the absorbable screws (mean, 0.3 N-m; SD, 0.19). The mean failure load for the metal screws (mean 640 N; SD, 201) was also significantly higher than for the absorbable screws (mean, 418 N; SD, 118).

Nerve regeneration during patellar tendon autograft remodelling after anterior cruciate ligament reconstruction: an experimental and clinical study.

The innervation of the rat and human anterior cruciate ligament, patellar tendon, and patellar tendon autograft after reconstruction of the anterior cruciate ligament was investigated by immunohistochemical and histological methods. A rat model of reconstruction with patellar tendon autograft was evaluated during active graft remodelling (2-16 weeks) and compared with normal ligament and tendon. The knees of 10 patients who had undergone reconstruction with patellar tendon autograft were examined 5-37 months postoperatively (remodeling fully completed) with arthroscopy and biopsy. As a control, biopsies from normal ligament and tendon were obtained from four patients. Nerve fibers were identified using antisera for protein gene product 9.5, a general neural marker. Neuronal regeneration was assessed by the expression of growth-associated protein 43/B-50. The sensory type of innervation was characterized by assessing the distribution of nerves containing the sensory neuropeptides calcitonin gene-related peptide and substance P. Immunoreactivity for all neural markers was found in both rat and human anterior cruciate ligament and patellar tendon. Two weeks after reconstruction, the rat autograft was acellular and no innervation could be identified. After 4 weeks, the grafts were viable, and immunoreactivity for protein gene product 9.5, growth associated protein 43/B-50, and calcitonin gene-related peptide was found until the 16th week postoperatively. Immunoreactivity for substance P was found in rat autografts at 4 weeks postoperatively only. All biopsies of human patellar tendon autograft showed signs of the remodelling process being fully completed, with revascularization and a sinusoidal collagen pattern with fibroblast repopulation. Neuropeptide immunoreactivity, however, was not found. The presence of immunoreactivity to sensory neuropeptides in the anterior cruciate ligament and patellar tendon may indicate a nociceptive and neuromodulatory function of these structures. The expression of sensory neuropeptides in the rat patellar tendon autograft suggests a possible involvement of sensory innervation during healing of the graft.

Effect of quadriceps or hamstring contraction on the anterior shear force to anterior cruciate ligament failure. An in vivo study in the rat.

We studied the effect of quadriceps or hamstring contractions on the anterior tibial shear load to anterior cruciate ligament failure in an in vivo rat model. In both knees of 20 Wistar rats the joint capsule and ligaments, except the anterior cruciate ligaments, were cut and the menisci resected. In 10 rats the right ligament was loaded to failure by anterior translation of the tibia relative to the femur in a testing device during hamstring contraction induced by electrical stimulation of the ischiatic nerve. In the other 10 rats, the right ligament was loaded to failure correspondingly during quadriceps contraction induced by electrical stimulation of the femoral nerve. The loading rate was 2.5 mm s-1 (approximately 0.6(-1)). The knee flexion during testing was 30 degrees. As control, the anterior cruciate ligament of the left knee was loaded correspondingly with relaxed muscles. The ultimate load for the ACL tested during hamstring contraction was 1.5 times higher than when tested with the hamstrings relaxed, more than double the energy was absorbed at failure and the linear stiffness was 1.2 times higher. During testing with quadriceps contraction, no differences in the structural properties were found, compared to testing with the quadriceps relaxed. Our findings show that hamstring contraction helps to resist anterior tibial shear force at 30 degrees knee flexion in rats thus protecting the anterior cruciate ligaments. Quadriceps contraction in this situation does not affect anterior shear force to ligament failure.

Contraction of knee flexors and extensors in skiing related to the backward fall mechanism of injury to the anterior cruciate ligament.

The purpose of this study was to examine the motion pattern and muscle activity during jumping and landing in downhill skiing to estimate the muscular involvement during the jump-landing-backward fall-anterior cruciate ligament (ACL) injury. A digitized 2-D video motion analysis and a synchronous 8-channel electromyography registration was performed over a jump on a downhill slope during 3 runs by 2 skiers and during 6 control jumps in the laboratory. The knee flexors (lateral gastrocnemius and biceps femoris) were recruited before touchdown and mean 60 ms earlier than the extensors (vastus lateralis and rectus femoris). Extensors and flexors reached peak activity simultaneously at the instant of landing. The knee flexion angle at the instant of landing was mean 36 degrees. As the landing was stabilized, the extensor activity persisted during eccentric work at increasing knee flexion as a corresponding flexor relaxation took place. The control jump in the laboratory showed a similar order of recruitment and timing of muscle contraction. The gastrocnemius was recruited mean 96 ms earlier and the biceps femoris mean 63 ms earlier than the extensors. This recruitment pattern during the landing movement suggest a learned motor program engaging the kinetic chain of the lower extremity to intercept the landing energy. The results also indicate that the knee flexor activity may protect the ACL at the instant of landing but that it is minimal shortly thereafter and probably not able to protect the ACL when a backward fall occurs. The knee was flexed substantially as the extensors became the dominating muscles. Thus, their ability to apply any anterior drawer force able to rupture the ACL is questioned.

Hamstrings and gastrocnemius co-contraction protects the anterior cruciate ligament against failure: an in vivo study in the rat.

An anesthetized rat model was used to study the effects of muscle contraction on the ultimate tensile load and the energy absorption at failure of the anterior cruciate ligament. In both knees, the joint capsule and ligaments, except for the anterior cruciate ligament, were divided, and the menisci were removed with the aid of a stereomicroscope. The cruciate ligament of the right knee was tested in tension until failure by femorotibial distraction during contraction of the hamstrings and calf muscles induced by electrical stimulation of the ischiatic nerve. The cruciate ligament of the left knee, which was loaded to failure with nonstimulated (relaxed) muscles, served as the control. The mean ultimate tensile load during muscle contraction was 86 N compared with 53 N when tested with relaxed muscles (p < 0.001). The energy absorption at failure was 0.41 and 0.19 J during contraction and relaxation, respectively (p < 0.05). This study suggests that previous investigations evaluating the force and energy necessary to rupture the anterior cruciate ligament (with use of a femur-anterior cruciate ligament-tibia complex stripped of all soft tissues and without gastrocnemius-hamstring muscle contractions) are incomplete and probably not representative of the in vivo situation.