Deformation and rupture of the articular surface under dynamic and static compression.

Cartilage-on-bone samples were dynamically and statically compressed at various stress levels to determine the deformation and rupture behaviour of the articular surface (AS). Instantaneous deformations were captured photographically by using a transparent indenter in combination with a ultra high speed flash. Principal strains (PS) were evaluated using large deformation theory. The tensile strains induced indirectly in the AS were a function of the rate at which the direct compressive force was applied. At the same compressive stress the tensile strains induced statically were approximately twice those induced dynamically. Rupture of the AS occurred in about 60% of those specimens tested statically at 15 MPa and followed approximately the split-line direction. By contrast, no rupture was observed dynamically even at stresses as high as 28 MPa. In terms of joint function the research demonstrates that the AS is considerably more resistant to rupture under dynamic than under static loading. The biomechanical parameter governing rupture appears to be the level of indirectly induced surface strain rather than the directly applied compressive stress. The very different mechanisms controlling the compressive deformation of articular cartilage (AC) at high vs low rates of loading clearly influence the levels of in-plane strain induced in the AS.

Why is the adolescent joint particularly susceptible to osteochondral shear fracture?

A biomechanical investigation of the dynamic shear failure of the osteochondral region of immature, adolescent, and mature bovine cartilage bone laminates was performed. The osteochondral junction was loaded in pure shear under impact conditions through the cartilage layer only. The results indicate the adolescent tissue fails at a nominal shear stress of 2.0 MPa, whereas the immature and the mature tissues fail at 3.8 MPa and 2.6 MPa, respectively. The adolescent tissue had a significant reduction in the fracture toughness of its osteochondral junction compared with that of the immature or mature tissues. The fracture toughness, describing the energy required to initiate and propagate a crack to failure, was 3.6 kN/m, 2.3 kN/m, and 10.2 kN/m for the immature, adolescent, and mature bovine tissues, respectively. This significant reduction associated with the adolescent osteochondral junction is explained in terms of the structural changes occurring within this important anchoring region during maturation. These findings question the wisdom of subjecting the adolescent joint to high levels and rates of loading.

Operative field contamination by the sweating surgeon.

BACKGROUND: There are a number of factors relating to the host, bacteria and wound that are important in the development of wound infection. The effect of the surgeon sweating has not been previously reported. METHODS: Ten surgeons performed a mock total hip joint operation under sterile conditions while not sweating and then repeated the operation while sweating. Settle plates were used to quantify the bacterial counts in the operative field in both phases. RESULTS: For each subject a mean of 3.3 colony forming units (c.f.u.) were present in the non-sweating phase and 6.9 c.f.u. were present in the sweating phase (P < 0.05). Organisms grown were normal skin flora. CONCLUSION: The sweating surgeon may be more likely to contaminate the surgical field than the non-sweating surgeon. It is important for orthopaedic surgeons, especially those performing joint replacement surgery, to be aware of this and to take measures to minimize sweating in the operating theatre.

Reamed versus unreamed femoral nails. A randomised, prospective trial.

We performed a randomised, prospective trial to evaluate the use of unreamed titanium nails for femoral fractures. Of 48 patients with 50 femoral fractures 45 were followed to union; 23 with an unreamed and 22 with a reamed nail. The study was stopped early because of a high rate of implant failure. The fractures in the unreamed group were slower to unite (39.4 weeks) than those in the reamed group (28.5 weeks; p = 0.007). The time to union was over nine months in 57% of the unreamed group and in 18% of the reamed group. In the unreamed group 14 secondary procedures were required in ten patients to enhance healing compared with three in three patients in the reamed group. Six implants (13%) failed, three in each group. Four of these six fractures showed evidence of delayed union. To achieve quicker union and fewer implant failures we recommend the use of reamed nails of at least 12 mm in diameter for female patients and 13 mm in males.

Assessment of foot movement.

A method of assessing foot movement suitable for use in clinical practice is presented. The method assesses the component of movement in the horizontal plane which is produced by rotating the calcaneum about the axis of the subtalar joint.

Delayed reconstruction of the calcaneal tendon.

Thirteen patients with ruptures of the calcaneal tendon diagnosed more than four weeks after injury were reviewed. Eleven patients had operative reconstruction with tendon shortening and the postoperative follow-up ranged from one to seven years. Isometric and isokinetic measurements, as well as the strength of the triceps surae, all compared favourably with the normal contralateral leg. Only one tendon re-ruptured. Eight of the eleven patients were satisfied with the results and the two patients who had refused reconstruction had worse functional results. Late reconstruction of a ruptured calcaneal tendon is thus a worthwhile procedure.

Closed fractures complicated by acute hematogenous osteomyelitis.

Osteomyelitis developed at closed fracture sites in two children. The infection responded to antibiotic therapy, and the fractures healed without chronic infection developing, impairment of bone growth, or loss of function. It is rare for a closed fracture to develop acute hematogenous osteomyelitis, but the diagnosis should be considered in a child with a closed fracture in whom a fever develops or who complains of increasing pain after the fracture has been reduced and immobilized. In children, the condition has an excellent prognosis.

Triplicate post-traumatic sciatic nerve palsy: evoked potentials in the diagnosis.

Three episodes of sciatic nerve palsy occurred after open reduction and internal fixation of a fracture-dislocation of the left hip and pelvis in a 20-year-old female injured in a motor cycle accident. There were also ipsilateral open fractures of the tibia and fibula and an open knee injury. When the palsy first developed the patient was in a hip spica plaster cast extending from the costal margin to encase the whole left lower limb. At the time of the second and third episodes of palsy she was in a left below-knee cast and it was not possible to fully assess the function of involved muscles clinically or electromyographically. Psychological factors due to prolonged disability and hospitalization were suspected as a possible cause of weakness. Therefore evoked potentials obtained by stimulation of the peroneal nerves were used to aid diagnosis. There was no response from lumbar and cerebral recording sites on stimulation of the peroneal nerve on the affected side. Diagnosis of a conduction block in the sciatic nerve was thus established. The patient recovered clinically and on repeated testing after motor recovery the cortical potential was attenuated and delayed by 15ms. Recurrent sciatic nerve palsy, occurring three times after hip trauma and with heterotopic bone formation and diagnostic application of evoked potential techniques, has not been previously reported.

The treatment of femoral fractures by cast-brace application and early ambulation. A prospective review of one hundred and six patients.

One hundred and six patients with 108 femoral shaft fractures were treated with a cast-brace. Ninety-eight cast-braces included an abdominal band and hip hinge. At follow-up three femora showed coronal malalignment that exceeded 9 degrees and sixty-nine showed varying degrees of sagittal malalignment (thirty-eight having anterior bowing and thirty-one, posterior bowing). Four patients regained only 100 degrees of knee flexion or less and four others had hyperextension of the knee of more than 10 degrees. Thirty-eight patients showed signs of knee instability but only four of them had symptoms of instability. Four fractures were treated operatively to correct excessive shortening or angulation and another fracture was bone-grafted to promote union. The mean shortening was 10.9 millimeters (standard deviation, 8.8 millimeters). Although the more comminuted of the eighty-five middle-third fractures shortened more than the others, the results of this method of treatment for these comminuted fractures were acceptable.

Shortening and angulation of femoral shaft fractures treated by cast brace application and early ambulation.

Twenty-eight patients with femoral shaft fractures were treated by early three piece cast brace application and ambulation. Unacceptable femoral shortening occurred in the first week after cast brace application in seven cases. When bony union occurred, shortening did not exceed length lost from telescoping. Fracture alignment either remained unaltered or changed to varus in response to weight-bearing on the third or fourth day after cast brace application. Fractures aligned in either valgus or varus in excess of 5 degrees while the patient was lying prone tended to malalign further in that direction as healing progressed. If roentgenograms obtained in the week after cast brace application demonstrate unacceptable shortening, bed rest and skeletal traction should be instituted. With the patient lying prone, if roentgenograms show coronal malalignment greater than 5 degrees, that should be corrected by thigh cast wedging.

Results of bone grafts in the treatment of tibial fractures.

In a retrospective study of 19 patients treated with bone grafts of the tibia, nine had ankle symptoms. Eight of the nine had synostoses between the tibia and fibula. Inasmuch as a synostosis is prone to develop after a posterolateral graft, this procedure should be used only when there is an unsatisfactory skin cover for the anterior surface of the tibia.

The effect of dihydroergotamine and heparin on the incidence of thromboembolic complications following total hip replacement: a randomized controlled clinical trial.

A randomized blind clinical trial was carried out to assess the effect of dihydroergotamine (DHE) alone and in combination with heparin on the incidence of thromboembolic complications of total hip replacement. It was found that a combination of DHE 0.5 mg and heparin 5000 units subcutaneously, given 8-hourly in separate injection sites, reduced the incidence of thromboembolic complications from 63 per cent in the untreated controls to 7.4 per cent in the treated group. This difference was highly significant. DHE alone produced a reduction in the incidence of thromboembolism but this reduction was not statistically significant. Blood loss was calculated using pre- and postoperative haemoglobin levels, taking into account the amount of blood transfused. It was found that the blood loss in the DHE/heparin-treated patients was identical to that in the untreated controls. The patients who received DHE alone had a significantly lower mean blood loss than the other two groups. It is concluded that this reduction in blood loss by DHE may be due to its venoconstrictor properties.

Birth injuries of the brachial plexus: incidence and prognosis.

Between March 1969 and May 1978, 36 babies sustained birth injuries of the brachial plexus at the National Women's Hospital, Auckland, New Zealand. This gives an incidence of 0.87 per 1000 live births. Nearly 80 per cent of these children had made a complete recovery by the age of 13 months, while none of those with significant residual defects has severe sensory or motor deficit of the hand.

Ipsilateral elbow and forearm injuries in children.

Twenty-five children with combined elbow injury and forearm bone fractures have been reviewed. The incidence of serious complications was low, and only one patient was significantly handicapped. Open reduction and internal fixation of the supracondylar fracture with closed treatment of the forearm fracture gave the best results.

Force and pressure recordings from patients with femoral fractures treated by cast-brace application.

Five patients with midshaft femoral fractures treated by early cast-brace application and ambulation were studied. With the patients in lying and standing postures, force transmitted through the knee hinges, ground reaction and pressure under the thigh cast were measured each week. When standing on the injured limb, the maximum load tolerated increased as the fractures healed and ranged from 39-61% body weight and 97-100% body weight at weeks two and eight respectively. In this posture in three cases, force transmitted across the knee hinges did not exceed 35% body weight or alter significantly throughout healing, the other two reached maxima of 67 and 60% body weight at week five and values decreased to less than 50% at week ten. By week six, each patient was transmitting significant force across the fracture (31, 12, 7, 36 & 55% body weight). Vertical force on the thigh cast due to rigid soft tissue containment was calculated to be between 3.6 and 10.8 X 9.8 Newtons throughout healing in all cases. Force transmitted through the knee hinges and pressure under the thigh cast, increased linearly as the injured limb was loaded.

Neurological complications, following lumbar radiculography with Dimer X.

Three cases developing increasing neurological deficit within 24 hours of lumbar radiculography with Dimer X are reported. All three developed severe low back and sciatic pain, and myoclonic spasms within one hour of the examination. In each a large intervertebral disc prolapse was outlined. Two cases developed near complete paraplegia before surgical decompression. Following surgery, two patients made a complete rapid recovery, and the other has recovered partially.

The treatment of femoral fractures by cast-brace and early walking: a review of seventy-nine patients.

Seventy-nine cases of fracture of the femoral shaft treated by cast-brace and early walking have been reviewed. Discrepancy in femoral length was assessed by scanogram. The cases were analysed to relate the incidence of shortening greater than 2 centimetres to the type and site of the fracture, and the time which elapsed from injury until the cast-brace was applied. Such shortening was encountered most frequently when the cast-brace was applied within the first two weeks from injury or after six weeks and in those patients with comminuted fractures of the middle third of the femoral shaft.

Pressures generated in the thigh muscles and under the thigh cast of an uninjured subject wearing a cast-brace.

Intrinsic pressures within the thigh muscles of a normal subject were recorded with the subject in five different postures before and after application of a cast-brace. The extrinsic pressures between the plaster cast and the underlying skin also were recorded. The intrinsic muscle pressures were significantly increased when the cast-brace was applied.