Introduction

Highly cross-linked ultrahigh molecular weight polyethylene (UHMWPE) is the most common bearing surface used in total joint arthroplasty due to its excellent wear resistance. While radiation cross-linking is currently used, cross-linking using a cross-linking agent such as a peroxide can also be effective with improved oxidative stability, which can be achived by an antioxidant such as vitamin E. The peroxide cross-linking behavior of UHMWPE in the presence of vitamin E was unknown. We investigated the cross-linking behavior and the clinically relevant mechanical and wear properties of peroxide cross-linked, vitamin E-blended UHMWPE.

Background

Post operative analgesia is an important part of Total Knee Arthroplasty (TKA) to facilitate early mobilisation and patient satisfaction. We investigated the effect of periarticular infiltration of the joint with chirocaine local anaesthetic (LA) on the requirement of analgesic in the first 24 hrs period post op.

Many pedicle screw instrumentation systems are currently available to the spine surgeon. Each system has its unique characteristics. It is important for the surgeon to understand the differences in these pedicle screw systems¹

Following the introduction of a new spinal instrumentation set to our clinical practice we encountered two cases of pedicle screw breakage. We thus decided to investigate the mechanism of this screw failure (screw A) in these particular cases and to compare the biomechanical properties, through independent analysis, of a variety of pedicle screws from different manufacturers.

Samples of the broken pedicle screws were retrieved at surgery. Surface analysis of the fracture area using the electron microscope, demonstrated features consistent with fatigue fracture.

Pedicle screws of comparable size from a variety of manufacturers were gathered for independent analysis. Shadowgraph analysis was performed of each screw allowing multiple measurements to be taken of the screw’s geometry. Using this data stress concentration factors were determined demonstrating screw A to have larger values than all the other screws ranging from 2 – 3.6 times the nominal stress. The smaller teeth of screw A, spaced further apart than in the other screws, means that the large proportion of the load which would be carried by the threads is distributed over a smaller area resulting in higher stresses in the threads. The sharp corner at the root of the thread, acting as a stress concentrator, would become the focal point of these high stresses, and magnify them by 2 to 3.6 times.

These increased stresses most likely account for an increased susceptibility to fatigue fracture seen in screw A.

In conclusion it is important to be careful with the introduction and use of new pedicle screw materials and designs, that all the standard biomechanical testing has been performed to a satisfactory standard.

Knowing the physical characteristics of the available pedicle screw instrumentation systems may allow the choice of pedicle screw best suited for a given clinical situation.

Introduction: Duchenne’s Muscular Dystrophy (DMD) is a progressive sex linked recessive disease, predominantly involving skeletal muscle. Scoliosis is almost universal in patients with DMD. Surgical stabilization carries a significant risks and complications with peroperative mortality of < 6%. Cardiopulmonary complications along with severe intraoperative blood loss requiring massive blood transfusion are the major cause of morbidity

Aim: To evaluate the efficacy of single rod fusion technique in reducing the peroperative and post operative complications especially blood loss, duration of surgery and progression of curve

Material & Methods: Retrospective review – 14 patients with scoliosis secondary to DMD with an average age of 14.5 years (range, 11–17) underwent single rod fusion technique using Isola rod system and pelvic was not included in fixation. Blood loss was measured directly from the peroperative suction and post operative drainage, indirectly by weighing the swabs. Vapour free hypotensive anesthesia was used in all case. Progression of curve was monitored over a period of five years.

Results: The mean operative time was 110 min (range, 80 – 180). The average blood loss was 1.6L (range, 0.7 – 5). The mean follow up was 32 months (range, 4 – 60). There was no progression noticed in the curve on follow up. Two patients develop complications, one had loosening & migration of the rod, required revision and superficial wound infection treated with intravenous antibiotics.

Conclusion: In our experience, single rod stabilization is a safe and quick method of stabilizing the spine in DMD with less blood loss and complications compared to traditional methods.

Introduction: A retrospective evaluation of early results of arthroereisis.

Material and Methods: Eight feet in five patients with pathological flexible planovalgus deformity that had failed non-operative management were treated with subtalar arthroereisis using the Kalix prosthesis. Diagnosis include oblique talus (2), vertical talus (1), diplegia secondary to head injury (1) and type I neurofibromatosis (1). The average age of patients was 6.4 years (range 4–12), and average follow-up was 9.9 months(range 4–20). Outcome was assessed using clinical assessment of the foot axis and functional improvement and radiographic measurements of change in the talocalcaneal angle and talonavicular sag.

Results: Arthroereisis was never performed in isolation, additional procedure included achilles tendon lengthening (2), gastrocnemius recession (6), talonavivular and spring ligament plication (5) and split tibialis anterior tendon transfer (1). All patients had improvement of foot function and restoration of foot axis to a position parallel to the axis of progression. Restoration and maintenance of the talocalcaneal angle was excellent in all cases with preoperative average of 42 degrees (range 20–70), improved to a postoperative average of 23 (range, 0 – 40). Talonavicular sag improved from preoperative average of 16.5 degrees (range 0–32), to post operative average of 26 degrees (range 18–35). Complications include persistent first ray extension which required a Lapidus procedure (1), Ongoing minor discomfort (1). No patients or parents were dissatisfied.

Discussion: The preliminary report supports the use of this technique in selected cases. Sizing of the implant and intraoperative assessment of correction of deformity and balanced surgery are critical to success. It is a simple and rapid procedure with advantages over alternatives such as Osteotomy and fusion. Long term results need further evaluation.

In late presenting developmental Dysplasia of hip there is controversy as to the most appropriate method of treatment. The purpose of study was to determine the outcome following the non-operative and operative treatment for late presenting developmental dysplasia of hip.

Retrospective study. Inclusion criteria – (1) Unilateral DH (2) Diagnosed 6 months or more after birth (3) Minimum follow up of 2 years after treatment. 41 patients matched the inclusion criteria. 32 patients attended the follow-up clinic. Patients were divided into non-operative and operative group. Outcome instruments used include activities scale for kids (ASK), physical component of SF36 v2, centre edge angle and severin classification system, all validated scoring systems.

32 patients with mean follow-up of 7 (2–12_ years. Mean age at the time of follow-up was 9 (range 2.7 – 15) years. In our series, 15 patients received non-operative and 17 patients received operative treatment. On ASK, conservatively treated hips scored 72% and surgically treated hips scored 69%. (P-Value = > 0.05). On SF36 v2, mean value of physical function score (PFS) for both non-operative and operative group were 57.58 respectively (P Value > 0.05). Centre edge angle (CEA) of non-operative and operative group were compared with their contra-lateral normal sides (P Value > 0.05). According to Severin classification system, 7 hips were grade I, 8 were grade II in the non operative group and in operative group, 10 were grade II, 5 were grade III and 2 were grade IV. There were no major complications and only one (3%) hip developed avascular necrosis of hip.

On a medium term follow-up, despite some radiological abnormalities, most of the patients achieved good functional results following both non-operative treatments for late presenting DDH. There was no statistically significant difference in the development of hips either treated conservatively or surgically. Long term follow up studies are required in order to establish the true outcome of late presenting DDH treated either conservatively or surgically.