Summary

Application of RSA in supine and standing positions allows pelvic fracture stability to be measured more accurately than current techniques. RSA may enable a better understanding of these injuries.

Patients with pelvic and acetabular fractures have a high risk of developing thromboembolic complications. Despite routine screening, the risk of PE remains high and may develop in patients with negative DVT screening. The search for a means to identify the patient ‘at risk’ has been elusive.

537 consecutive patients, referred to Royal Adelaide Hospital over a 20 year period for treatment of pelvic and acetabular fractures, were evaluated prospectively for pulmonary embolus (PE). 352 patients referred directly to the author were treated with variable dose heparin as prophylaxis to venous thromboembolic (VTE) disease. 184 patients primarily admitted under the general surgeons or to ITU, prior to referral to the author, were treated with fixed dose heparin or Enoxaparin. All patients were followed prospectively to determine the rate of pulmonary embolus. The heparin dosage requirements of those who developed pulmonary emboli were compared to those who did not. Patients were also identified for whom a clinical diagnosis of deep venous thrombosis (DVT) was made during the study and their heparin dosage requirements were determined.

7 of 352 patients treated with variable dose heparin developed PE (1.98%). 13 of 184 patients treated with fixed dose heparin, Enoxaparin, or combinations, developed PE (7.06%). An incidental finding of DVT was made in 36 patients. Of these, 10 patients (2.8%) were treated with variable dose heparin and 26 patients (14.1%) with fixed dose heparin or Enoxaparin.

The average Injury Severity Score was higher in patients treated with variable dose heparin than those treated with fixed dose regimes. Patients treated with variable dose heparin who developed PE showed a progressively increasing heparin requirement. The majority of patients who did not develop PE (72%) showed a progressively decreasing heparin requirement (suggesting reversal of a prothrombotic state). 21% showed an initial increasing heparin requirement followed by a decreasing requirement (suggesting a prothrombotic state that was reversed, e.g. a DVT successfully treated by the increasing heparin dose provided by a variable dose regime). 4% manifested a static heparin requirement (suggesting maintenance of a prothrombotic state). 8 patients treated with variable dose heparin developed DVT. 6/8 patients manifested a phase of progressively increasing heparin requirement, followed by a decreased requirement, and 2/8 patients manifested a sustained level of heparin requirement.

Patients with pelvic and acetabular fractures treated with variable dose heparin showed a rate of PE (1.98%). This is remarkably low compared with published rates of PE in such patients, and particularly compared with those patients treated only with chemoprophylaxis. The rate of PE was 3.5x higher and the rate of DVT was 5x higher in patients treated with fixed dose heparin or Enoxaparin. Patients who developed PE or DVT manifested an increasing heparin requirement. An increasing dosage of heparin may protect the ‘at risk’ patient from venous thromboembolism. Fixed dose unfractionated heparin/LMWH may be insufficient to treat the ‘at risk’ patient. An increasing heparin requirement may identify the patient ‘at risk’.

Open reduction and internal fixation of tibial plateau fractures is traditionally performed through an anterior, anterolateral or an anteromedial approach and more recently a posteromedial approach. These approaches allow satisfactory access to the majority of fracture patterns with the exception of posterolateral tibial plateau fractures.

To improve access to posterolateral tibial plateau fractures, we developed a posterolateral transfibular neck approach that exposes the tibial plateau between the posterior margin of the iliotibial band and the PCL. The approach can be combined with a posteromedial and/or an anteromedial approach to the tibial plateau. Since April 2007, we have used this approach to treat nine posterolateral tibial plateau fractures. All cases were followed up prospectively. Fracture reduction was assessed on radiographs, CT scans and arthroscopicaly. Maintenance of fracture reduction was assessed with radiostereometric analysis. Clinical outcomes were measured using Lysholm and KOOS scores.

Anatomic or near anatomic reduction was achieved in all cases. All fractures healed uneventfully and no loss of osteotomy or tibial plateau fracture reduction was identified on postoperative plain X-rays. In the cases monitored with radiostereometric analysis, the fracture fragments displaced less than 2 mm during the course of healing. All osteotomies healed either at the same rate or quicker than the tibial plateau fractures. There were no signs and no symptoms of lateral or posterolateral instability of the knee during or after the healing of the osteotomy. There were no complications related to the surgical approach, including the fibular head osteotomy. All wounds healed uneventfully and there were no symptoms related to the CPN. The patient reported outcomes recorded for this group at six months, using the Lysholm score (mean 71, median 77, range 42–95), compared favourably to the entire cohort of 33 patients treated operatively at our institution for a tibial plateau fracture and followed up prospectively during the same time period (mean 64, median 74, range 20–100).

The posterolateral transfibular approach for lateral tibial plateau fractures is an approach that should be considered for a certain specific pattern of fractures of the lateral tibial plateau. Our preliminary results demonstrated no complications through the learning curve of the development of this technique.

Differentially loaded radiostereometric analysis (DLRSA) uses RSA whilst simultaneously applying load to the bones under investigation. This technique allows measurement of interfragmentary translations and rotations under measured amounts of weight bearing. The aim of this paper was to measure the mechanical stiffness of distal femoral fractures during healing.

Six patients with a 33A2, 33A3, 33B2 and 33C2 fracture were treated with open reduction, internal fixation using a long bridging plate. All patients had a DLRSA examination at 6, 12, 18 and 26 weeks postoperatively. Each DLRSA examination consisted of RSA radiographs taken without load (pre-load), under different increments of load, and finally, without load (post-load). The direction and magnitude of the interfragmentary displacements in six degrees of freedom were recorded at each examination.

DLRSA examinations were able to monitor the inter-fragmentary displacements of the distal femoral fragment relative to the femoral shaft. The interfragmentary displacement recorded, progressively increased as more load was applied in all patients, at all follow-up time points. The two dimensional (2D) translations under maximum tolerated load, progressively decreased over time in three patients. The 2D translations recorded under 60 kg of load at 26 weeks for these patients was 0.18, 0.21 and 0.27mm. The 2D translations of two patients did not decrease progressively between 6 and 18 weeks but did decrease at 26 weeks to 0.47 and 0.75mm. One patient recorded 2D translations of 4.11, 3.48 and 4.53mm under 30kg at 12, 18 and 26 weeks respectively. In the majority of examinations, post-load radiographs enabled the interfragmentary displacements under load to be identified as elastic in nature.

The DLRSA stiffness data confirmed that at 26 weeks three patients had united; two were delayed but improving; and one was a clear non-union without progression. DLRSA examinations may be used as a clinical research tool. to monitor in vivo the stiffness of healing femoral fractures fixed with “relative stability”.

Differentially loaded radiostereometric analysis (DLRSA) uses RSA whilst simultaneously applying load to the bones under investigation. This technique allows measurement of interfragmentary translations and rotations under measured weight bearing and joint movement. We have recently introduced this technique to monitor tibial plateau fracture healing. This paper presents our preliminary results.

Twelve patients with a 41 B2, B3, C2, or C3 fracture were followed for a minimum of three months. RSA beads were inserted in the largest osteochondral fragment and the adjacent metaphysis. Knee flexion was restricted to 60° for 6 weeks. After partial weight bearing (20kg) between 2 and 6 weeks, patients progressed to full weight bearing. Follow up included clinical and radiological examinations and patient reported outcome scores (Lysholm, KOOS). DLRSA examinations included RSA radiographs in 60° flexion and under measured weight bearing. Significant interfragmentary displacement was defined as translations greater than 0.5mm and/or rotations greater than 1.5°.

There was no loss to follow-up. Longitudinal RSA follow-up: Follow-up RSA radiographs were compared to postoperative examinations. Osteochondral fragment depression was less than 0.5mm in seven patients and between 2 and 4mm in the remaining five patients. Significant interfragmentary displacement after three months was recorded in three patients. DLRSA flexion results: Under 60° of flexion, translations over 0.5mm were recorded in five patients (one postoperatively; one at 2 weeks; two at 6 weeks; and one postoperatively, at 2 weeks and at 3 months). Rotations over 1.5° were recorded in six patients (one postoperatively; two at 2 weeks; one at 6 weeks; one at 2 weeks, 3 months and 4.5 months; and one postoperatively, at 2 weeks, 3 months and 6 months). DLRSA weight bearing results: Under partial weight bearing at two weeks, two patients recorded significant translations, one involving a significant rotation. Under weight bearing as tolerated, three patients recorded significant translations (one at 6 weeks; and two at 18 weeks) and four patients recorded significant rotations (one at 6 weeks; one at 18 weeks; and two at 12 and 18 weeks). Patient Reported Outcomes: Both the Lysholm and KOOS scores improved between 6 weeks and 3 months. DLRSA provides new insight and perspective in tibial plateau fractures. Some fractures take more than three months to heal. Our current rehabilitation protocol was safe in most patients, however significant interfragmentary displacement was encountered in 17% at the 2 week followup, raising questions about the quality of the initial stability.

1. The effect of removal of mechanical loads from bone. Lanyon and various co-workers studied functionally isolated avian bone preparations to which external loads could be applied in vivo through external fixation devices. They showed that the application of a rigid external fixator unloaded the bone, and that this stress shielding resulted in a substantial remodelling of the bone on three fronts: endosteal, cortical and, to a lesser extent, periosteal. The balance of remodelling was negative, resulting in a net loss of bone mass.

Similar results with rigid external fixation have been reported in other animals. These findings are consistent with what we know about disuse osteoporosis resulting from muscular inactivity and reduction in weight bearing. Clinically such bone atrophy commonly occurs: after a fracture necessitating various degrees of immobilisation; after muscle inactivity due to diseases of joints and muscle, or bed rest; after long-standing systemic debilitating disease; after muscle paralysis; and after periods of weightlessness in space.

The results are also consistent with what we know about bone that is unloaded by various fixation devices. Woo and his colleagues have shown that in intact bone, fixed with a stainless-steel plate, there is significant stress shielding and that this results in loss of bone mass. Similar results have been reported by other investigators.

Likewise, in fractures fixed by rigid plate fixation there is similar stress shielding, which again results in loss of bone substance, together with persistence of woven bone at the fracture site.

Bone remodelling is very sensitive to small changes in cyclic bone stresses and changes representing less than 1% of ultimate strength can cause measurable differences in bone atrophy after a period of months.

Experimental studies have shown that greater bone remodelling and bone loss is observed when the rigidity of fracture fixation is increased.

Progressive bone loss may occur after fixation of fractures with metal plates. This leads to an ubiquitous clinical dilemma: if the plate is removed too early, fracture may occur because of insufficient union, whereas if the plate is removed too late, re-fracture may occur because of structural weakening and loss of bone mass.

In summary, removal of mechanical loads from bone, whether it be physiological, by rigid plate fixation or by rigid external fixation, results in negative remodelling and a net loss of bone mass.

2. Effect of cyclic mechanical loads on intact bone. Rubin and Lanyon, again using isolated avian bone preparations, found that the application of a cyclic load of only four consecutive cycles a day prevented negative bone remodelling and resulted in no change in bone mass. This suggested that a suitable strain regimen prevented remodelling. Furthermore, they found that 36 consecutive cycles per day not only prevented cortical resorption, but also resulted in substantial periosteal and endosteal new bone formation over a six week period. An increase in the number of strain cycles to 360, or 1800 provided no increased benefit.

That mechanical loading of intact bone results in cortical thickening and increased bone deposition has been confirmed by other studies. Physiological loading of intact bone produces the same increased bone deposition in laboratory animals. Similar effects have been shown in humans, for example, in tennis players, baseball pitchers and cross country runners, as well as in other sportsmen.

Resection of the radius or ulna, thereby increasing the load of weight bearing in the remaining bone, has been shown to result in hypertrophy of that bone in dogs and in various animals.

Fixation of fractures with less-rigid fixation results in healing with external callus formation, and earlier weight bearing.

In summary, these studies have shown that, in animals or humans, the application of physiological levels of strain to bone, either physiologically or mechanically, causes remodelling which results in a net gain of bone mass.

3. Effect of static mechanical loads on intact bone and fractures. Using the same avian model, Lanyon and Rubin showed that static loads of similar physiological magnitudes of strain did not have a positive influence on the remodelling process. Hart, Wu, Chao and Kelly obtained similar results using external fixators. They concluded that static compression increased the rigidity of fixation but, of itself, provided no direct benefit for bone healing. Anderson studied compression plate fixation and the effect of different types of internal fixation and reported no evidence of stimulation of osteogenesis by compression. Other researchers have reported similar findings.

The effects of static compression produced at the fracture site by plate fixation have been reviewed extensively. Some investigators have claimed that compression promotes fracture healing, but there is no evidence of this from paired comparisons in the literature.

In summary, static compression does not directly stimulate fracture healing.

4. Effect of cyclic mechanical loads on fractures. Yamagishi and Yoshimura showed in 1955 that intermittent compression forces applied to healing fractures in rabbits caused proliferation of cartilaginous callus. In 1981 Wolf and co-workers reported that when long bone fractures were treated with cyclic loading, bone strength increased more rapidly than when fractures were treated by constant compression. In 1985 Goodship and Kenwright published their work on the influence of induced cyclic micromotion on the healing of experimental tibial fractures, using an Oxford External Fixator. When 500 cycles were applied per day, they found that the micromotion produced external callus sooner, namely at one week, compared with static external fixation where callus was just commencing at three weeks. The micromotion resulted in more callus formation, which extended over a wider portion of the diaphysis. Consequently, they found that fracture stiffness increased at a greater rate in the stimulated group than in the rigid group. When the animals were sacrificed at twelve weeks they found that there was increased torsional stiffness in the stimulated group, ie. 83% of the intact control stiffness, compared with 54% in the rigidly-fixed group.

These findings have been replicated by others. Yamagishi and Yoshimura, as well as Woo and co-workers, have shown that those models which allowed some fracture movement produced proliferative external callus formation. This callus was inhibited proportionally as the rigidity of the fixator was increased. Similar studies have been performed in humans. Kenwright, Goodship and co-workers showed that controlled axial cyclic micromotion decreased the time to full weight bearing, compared with rigid tibial fixation33, and further studies showed the same findings.

In summary, both animal and human studies have shown that the application of controlled cyclic micromotion to fractures promotes bone healing.

5. Summary and application. An understanding of the manner by which various loading regimes affect bone formation and fracture healing allows the treating physician to plan effective treatment of fractures. It forms a rationale for total perioperative management of patients, in terms of the choice of treatment, the choice of implant, the weight-bearing status and the timing of physical activity. It has also lead to the concept of ‘dynamisation’ of fractures and the development of second and third generation external fixators.

Aim: To establish a method of emergency and definitive stabilisation of Type C pelvic ring injuries.

Methods: Patients with pelvic ring disruption were treated acutely, using instrumentation developed by Dr. Charles Reinert. Patients were positioned supine on a radiolucent operating table configured to allow the C-arm of an image intensifier to swing through an arc sufficient to allow pelvic inlet and outlet views of the pelvis. The unstable hemipelvis was reduced by means of longitudinal traction on the leg and lateral compression with a spiked, long handled, cannulated guide. Guide wires could be positioned accurately through the guide, allowing accurate placement of AO 7.3 mm cannulated iliosacral screws, by minimally invasive percutaneous techniques.

Results: Successful acute biomechanical pelvic stabilisation was achieved in all cases. After a short learning curve, the procedure could be completed in 20 minutes.

Discussion: Previously, pelvic stabilisation was often achieved by initial, tentative stabilisation using pelvic slings, traction and external fixation, with or without later definitive fixation. Using minimally invasive techniques, rapid, emergency stabilisation can be achieved, with sufficient stability to equally suffice for definitive fixation. The minimally invasive, percutaneous technique provides greater safety for treatment of patients with early coagulopathy.

Conclusions: Acute, rapid and definitive stabilisation of type C pelvic ring disruption can be achieved by minimally invasive, percutaneous techniques using the Reinert instrumentation.

Introduction: Type C pelvic ring disruptions are commonly associated with significant patient morbidity. It is the senior author’s (APP) experience that the sacro-iliac alar cartilage is commonly damaged at the time of initial trauma. If left untreated, this may give rise to post-traumatic arthrosis of the joint, with resultant pain. The natural history of type C disruptions is one of late pain. In this paper, we review our results of acute arthrodesis of the SI joint simultaneously with fixation of the posterior pelvis.

Methods: From 1987–2000, a consecutive series of 28 patients who underwent primary surgical fusion and internal fixation of the sacro-iliac joint underwent clinical and radiographic review. All patients were examined at latest follow-up (79.8 months) in regards to pain, range of motion, walking tolerance and the incidence of significant complications. Evaluation of the pelvic ring reduction and success of arthrodesis of the SI joint were made through radiographs of the pelvic ring. In addition patients completed the SF-36 as a measure of general health status and the Musculoskeletal Function Assessment (MFA) and WOMAC scores as a measure of functional outcome. Work status was also examined.

Results: The majority of these injuries were sustained in either motor vehicle crashes or high energy falls. There was a high incidence of associated injuries and co-morbidities. The male to female ratio was approximately 2:1 with a mean age of 27 years. At initial surgery, all patients were noted to have severe fragmentation and disruption of the alar cartilage. The majority of patients had sacro-iliac screw fixation for their posterior injury and an external fixator for anterior stabilization. At follow-up there was a low incidence of late posterior complex pain. All patients were independently mobile and there were minimal complications. Only 1 patient had to change jobs secondary to pelvic or low back pain. The functional outcome at long term follow-up was good with regards to the SF-36, MFA and WOMAC scores.

Conclusions: Type C pelvic ring injuries have a high incidence of disruption of the alar cartilage. Treatment of these injuries by primary fusion and internal fixation leads to good long-term results.