Femoral fracture following knee ligament reconstruction surgery due to an unpredictable complication of bioabsorbable screw fixation: a case report and review of literature
© Springer-Verlag 2009
Received: 24 May 2009
Accepted: 17 November 2009
Published: 17 December 2009
We report an unusual case of femoral fracture from minimal trauma, due to the rapid disappearance of a bioabsorbable interference screw used for reconstruction of the posterolateral corner of the knee. The literature on bone tunnel fractures following knee ligament reconstruction surgery is also reviewed.
Interference screws used for knee ligament reconstructive surgery are a popular application of bioabsorbable materials in orthopedics. They offer various advantages [1, 2] over traditional metallic implants, such as the ability to engineer them to provide an optimum degradation profile, a reduced need for implant removal, and less distortion on magnetic resonance imaging (MRI).
Polylactide carbonate (PLC) is a combination of an amorphous bioabsorbable polymer, poly DL-lactide-coglycolide (PDLG), with calcium carbonate, a bone-stimulating material and neutralizing agent . PLC was used to develop the “Calaxo” (Smith & Nephew, Andover, MA, USA) interference screw for knee ligament reconstruction surgery.
Consent was obtained from the patient to publish his case. A 26-year-old man underwent arthroscopic reconstruction of his anterior cruciate ligament (ACL), posterior cruciate ligament (PCL) and posterolateral corner following a multiple-ligament knee injury obtained while playing rugby. The patient had undergone a twisting knee injury during a tackle and was immediately diagnosed as having a severe knee injury and referred to the senior author (FSH). An MRI scan performed within twenty-four hours of the injury confirmed a tear of the ACL, PCL and posterolateral corner.
Surgical technique of ligament reconstruction
Postoperatively the patient was mobilized nonweight-bearing for 2 months in a knee brace, and specialist physiotherapy was initiated for muscle strengthening and range of movements. After 2 months he was allowed to weight-bear. His brace was removed after 16 weeks.
The main disadvantages associated with the use of bioabsorbable implants are their comparatively low mechanical strength, their relatively high cost, and the undesirable biological response  they may produce. The persistence of bioabsorbable screws for up to 3 years after their insertion is well documented in MRI studies after knee ligament reconstruction surgery [4–6].
In ovine models , the PLC screws have shown gradual and controlled degradation, stimulating ossification of the graft within the bone tunnel. New bone thus formed was noted around the margin of the screw as early as 6–12 weeks. This was followed by partial integration of the screw with bone by 26 weeks and complete replacement with new bone at 52 weeks. Computed tomography data followed this pattern, with extensive integration of the screw to bone by 26 weeks and disappearance of the screw by 52 weeks. An interference screw that would replenish the bone tunnel would be an ideal choice for knee ligament reconstruction surgery. However, clinical studies looking at the outcome of PLC screws are lacking.
Time from procedure
Noah et al. 
Patellar tendon ACL reconstruction and ITB extra-articular tenodesis
Ternes et al. 
GORE-TEX graft ACL revision
Wiener and Siliski 
Patellar tendon ACL revision
Manktelow et al. 
Hamstring tendon ACL reconstruction with extra-articular tenodesis
24 months fracture from staple of extra-articular augmentation to intraosseous tunnel
Berg et al. 
BPTB ACL reconstruction
Radler et al. 
ACL reinsertion and LAD. Latter removed after 5 months
6.5 mm cancellous screw
Mithoefer et al. 
Patellar tendon ACL reconstruction
7 × 25 metal interference screw for a 10 mm tunnel
5 months. Fall and hyperextension injury
Wilson et al. 
BPTB ACL reconstruction
Interference screw, ? size
9 months, fall
Sheps et al. 
Quadrupled ST-G autograft ACL reconstruction
5 months, head injury, ? fall
In the case reported by Manketelow et al.  in 1998, the fracture extended from the staple of the extra-articular augmentation to the intraosseous tunnel, 24 months after a hamstring autograft ACL reconstruction with extra-articular tenodesis. In a case reported by Ternes et al.  in 1993, the femoral tunnel used for the placement of a GORE-TEX prosthetic graft was the site of the fracture, which occurred 8 weeks following the procedure. Multiple anterolateral femoral cortex perforations were reported as the etiology for the fracture reported 7 months following a patellar tendon ACL reconstruction by Weiner et al.  in 1996, and 5 months following quadrupled hamstring graft ACL reconstruction by Sheps et al.  in 2006. Berg et al.  in 1999 reported a fracture through the femoral tunnel 8 weeks after a bone—patellar tendon—bone ACL reconstruction. At the time of the operation, the femoral tunnel had been over-drilled and the cortex had been perforated. The femoral tunnel was itself noted to be the stress riser, precipitating a fracture 5 months following patellar tendon ACL reconstruction by Mithoefer et al.  in 2005, and 9 months following a similar procedure by Wilson et al.  in the same year.
Tibial plateau fracture
El-Hage et al. 
Achilles tendon ACL reconstruction
Richards interference screw
18 months post-trauma
Morgan and Steensen 
Delcogliano et al. 
Patellar tendon ACL reconstruction
10 mm tibial tunnel and 9 × 25 interference screws
Mithofer et al. 
BPTB ACL reconstruction
Post and washer
7 months. Fall down stairs and twisting knee injury
Sundaram et al. 
8 mm tunnel fixed with 9 × 25 RCI screws
12 months, fall
Thaunat et al. 
11 mm tunnel, 9 mm PGA-co-TMC screw
4 years, valgus compression injury after fall
Biomechanical studies have shown that a bone defect such as a screw hole can concentrate stress and decrease the bone strength to torsional loading [22–24]. This may explain the fractures noted in the osseous tunnels following knee ligament reconstruction surgery.
Both mechanical and biological factors have been recognized to contribute to tunnel enlargement after ACL reconstruction . Mechanical factors include motion of the graft within the tunnel, fixation methods/devices, stress shielding of the graft, improper graft placement, and accelerated rehabilitation. Graft swelling, the use of allograft tissue, synovial fluid propagation within bony tunnels, and increased cytokine levels within the knee are all biologic modes of osteolysis contributing to tunnel enlargement. In most cases tunnel enlargement is minimal after 3 months . Unpredictable bioabsorbable screw resorption results in graft in empty tunnel and perhaps synovial reaction and cytokines, all contributing to persistent tunnel enlargement and bone weakening.
In our case, rapid degradation of the PLC screws in the osseous tunnel in the absence of any attempted bone integration may have predisposed to the fracture by a similar mechanism. Ongoing clinical concerns with the unpredictable absorption of the PLC screws (Calaxo, Smith & Nephew) lead to their withdrawal from the market in 2007. It is crucial to be aware of adverse effects where this particular interference screw has been used.
In conclusion, stress risers may occur following the use of bioabsorbable screws for ligament reconstruction surgery, particularly if screw resorption is rapid and bone integration is not complete.
Femoral fracture presenting as a late complication following the use of bioabsorbable interference screws in knee ligament reconstruction surgery is rare. It is important to be aware of this potential postoperative complication when considering which form of screw fixation to use.
Conflict of interest statement
No conflicts of interests or disclosures.
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