To evaluate and describe the plain radiographic changes observed with time in fusions using SiS-CaP. We describe, for the first time, 4 stages of bone substitute fusion mass (BSFM) radiographic appearance in relation to time post-op.

Retrospective, radiological evaluation.

Over 200 plain radiographs were evaluated. 70 consecutive fusions for degenerative spinal stenosis were included, in all cases performed by the same surgeon using the same operative technique. Follow-up was from 3 months to 2 years post-op.

Radiographs were evaluated for the presence or absence of SiS-CaP granules, bone formation and for evidence of pseudarthrosis.

Trends were seen within the BSFM with respect to time. At 6-12 weeks post-op a ‘homogenous granular stage’ indicates the presence of the unchanged SiS-CaP.

At 12 weeks, small pockets appear within the BSFM in the ‘vacuolation stage’, indicating bioresorption of the graft. Vacuoles become increasingly radio-opaque indicating bone proliferation during the ‘homogenous lamellar stage’. At variable time between 6 months and 2 years, the BSFM becomes encapsulated in the ‘cortication stage’ visible as a sclerotic rim around the BSFM.

We have seen a clear trend in the behaviour of the fusion mass in this case series. The radiological stages we have described above can be closely correlated with previously reported in-vitro and in-vivo studies looking at the micro-function of SiS-CaP. We hope that this description will help to judge the progress of graft incorporation and fusion. Further study of inter and intra-observer correlation will be required.

To assess radiological fusion rates in posterolateral fusions using SiS-CaP.

Retrospective, radiological follow-up study.

Single surgeon series of 76 consecutive patients were evaluated, in a regional spinal unit. All patients had clinical and radiological (MRI) spinal canal stenosis secondary to degenerative spondylosis or spondylolisthesis. Surgery consisted of instrumentation, decompression and meticulous preparation of the posterolateral graft bed by removal of all soft tissues posterior to the inter-transverse membrane and decortication of transverse processes (TPs). SiS-CaP putty was injected into this gutter and moulded around the instrumentation. Good quality, well prepared bone chips from the posterior decompression were seeded into the putty. Patient radiographs were reviewed at 3-6 months, 1 year and 2 years.

Radiographs were assessed using a protocol to examine granularity, bone formation and evidence of pseudarthrosis, based upon previously reported literature ¹ and our personal experience.

Of the 76 patients, 26 were excluded. M:F was 21:29. Mean age was 58yrs. Average number of motion segments fused per case was 2.2. There was one pseudarthrosis with metalwork fracture, and thus a total fusion rate of 98%. In addition, one patient had scanty bridging of TPs, and one patient had lucency around the S1 screws.

SiS-CaP, as a bone graft substitute in posterolateral instrumented fusions, gives comparable results to published fusion rates using autologous iliac crest grafting and/or Bone Morphogenic Protein ². Moreover, it avoids the associated morbidity of iliac bone harvest.

Introduction: Anterior cruciate ligament (ACL) rupture impairs knee stability. Reconstruction of the ACL is therefore performed to restore knee stability and avert risk of subsequent ligament and meniscal injury. Bone-patellar tendon-bone autograft is the most commonly employed technique for ACL reconstruction and considered the “gold standard”. Although 10% postoperative patellar tendon shortening has been reported with this technique, there are no systematic studies assessing the effect of this shortening on patellofemoral joint (PFJ) biomechanics under loading conditions simulating normal physiologic activity. The purpose of this study was to determine if 10% shortening of the patellar tendon affected PFJ biomechanics.

Methods: Patellofemoral contact characteristics were evaluated in cadaveric knees before and after patellar tendon shortening. Tendon shortening was performed using a specifically designed device that shortened the tendon without interfering with its anatomic and physiologic integrity. Conditions simulating light physical activity such as level walking were recreated by applying physiological quadriceps loads and corresponding angles of tibial rotation to the PFJ at 15°, 30° and 60° of knee flexion. PFJ contact areas were measured at each position of knee flexion before and after patellar tendon shortening using the silicone oil-carbon black powder suspension squeeze technique (3S technique, Yao & Seedhom, Proc Instn Mech Engrs1991;205:69–72). Differences were compared using the Wilcoxon signed rank t-test, with p< 0.05 required for statistical significance.

Results: Twelve unembalmed cadaveric knees (median age 81.8 years, 8 female: 4 male) were available for study. Five knees had evidence of osteoarthritic changes, and were rejected. The remaining 7 knees were macroscopically intact and were considered adequate for the experimental procedure. The mean patellofemoral contact areas and stresses determined preoperatively were comparable to those reported in normal knees in previous studies. Following patellar tendon shortening, PFJ contact areas were displaced superiorly on the patellar articular surface and distally on the femoral articular surface. Although the PFJ contact area increased by 17% at 15° of knee flexion (p=0.04), no significant change occurred at 30° or 60° of knee flexion (p> 0.05). Patellofemoral contact stress did not differ before and after patellar tendon shortening (p> 0.05) at any angle of knee flexion.

Conclusions: Our results suggest that with light activity such as level walking, a 10% postoperative shortening of the patellar tendon does not alter patellar tracking (in particular contact stresses) and therefore may not impact biomechanics of the patellofemoral joint. Extrapolating these results to the clinical scenario, deleterious consequences on the patellofemoral joint are unlikely after bone-patellar tendon-bone autograft reconstruction of the ACL despite the possibility of postoperative patellar tendon shortening.

Introduction: Isolated PCL ruptures are most frequently treated non-operatively, although PCL deficiency may ultimately lead to degenerative changes within the patellofemoral compartment. This study investigated, for the first time under physiological loading conditions, the change in patellar tracking as a result of PCL deficiency, hoping to further understand the clinical consequences in situations where such an injury is treated conservatively.

Method: Using eight fresh cadaveric knees, physiological axial tibiofemoral loads and rotatory torques occurring during level walking, were applied to determine tibial rotation angles. These were then used under dynamic Quadriceps femoris loading to determine contact areas and stresses within the patellofemoral joint at 15°, 30°, 60° and 90° of knee flexion. The PCL was then severed, and the procedure repeated under the same loading conditions.

Results: Significant increases in patellofemoral contact stress in the PCL deficient knees were observed at 15° and 30° knee flexion, both in internal and external rotation of the tibia (TABLE I). For these respective rotation positions the increases were 23% and 20% at 15°, and 19% and 28% at 30°, (in all cases p≤0.05). These significantly increased stresses coincided with unchanged contact patterns on the inferior third of the patella, spanning both its medial and lateral facets.

Conclusions: The increased stresses were due to increased patellofemoral joint reaction force, caused by a decreased angle between the quadriceps and patellar tendons due directly to posterior tibial translation in the PCL deficient knees. Significantly increased patellofemoral contact stresses at 15° and 30° of knee flexion, may be implicated in the degeneration of articular cartilage, on both the medial and lateral facets of the inferior third of the patella. These results point out the need for further biomechanical studies to investigate the effects of more strenuous loading conditions. There is also need for clinical studies to investigate focal lesions associated with long-term PCL deficiency.