April 1999 • Volume 15 • Number 3

Tibial and Pretibial Cyst Formation After Anterior Cruciate Ligament Reconstruction With Bioabsorbable Interference Screw Fixation

Vladimir Martinek, M.D. [MEDLINE LOOKUP]
Niklaus F. Friederich, M.D., Ph.D. [MEDLINE LOOKUP]


   Abstract  TOP 

Summary: We report a case of an osteolytic tibial enlargement in association with a pretibial cyst formation 8 months after successful anterior cruciate ligament reconstruction with autologous bone–patellar tendon–bone graft and tibial graft fixation with a bioabsorbable interference screw. No joint inflammatory reaction or graft insufficiency was detected. The patient underwent cyst excision and curettage of the tibial tunnel with full recovery and return to preinjury level of activity 2 months after the revision surgery. To our knowledge, the reported complication is the first obvious adverse reaction to a poly-D,L-lactide interference screw in anterior cruciate ligament surgery.

Key Words: Anterior cruciate ligament, Reconstruction, Bioabsorbable interference screw, Cyst, Complication.

Interference screws have become a popular fixation method in anterior cruciate ligament (ACL) reconstruction with bone–patellar tendon–bone (BPTB) grafts. Using the original metal interference screws, some complications were reported in initial and revision surgeries.1-3 Bioabsorbable interference screws have been hypothesized to eliminate some disadvantages of metal screws and to improve the postoperative graft imaging.4-6 New types of polymer materials have been developed in recent years to avoid adverse reactions that were seen after internal fixation of intra-articular fractures or shoulder stabilization with absorbable fixation device.2,5,7-9 To date, no serious adverse reactions in the knee have been reported using the new generation of poly-d,L-lactide bioabsorbable interference screws for graft fixation in ACL reconstruction.2,10

We present a case of ACL reconstruction with autologous BPTB graft and bioabsorbable interference screw fixation in which an osteolytic cyst formation in the osseous tibial tunnel, communicating with a symptomatic pretibial cyst at the tibial tunnel aperture, was noted. To our knowledge, this is the first reported complication in association with a poly-D,L-lactide interference screw in the knee joint.


A 32-year-old man sustained an isolated ACL disruption of his left knee while playing soccer. Postprimary arthroscopic ACL reconstruction with autologous BPTB using a 2-incision press fit technique (Burkart P, personal communication, 1995) was performed because of significant instability with grade 3 positive Lachman test and grade 2 positive pivot shift. In this technique, the BPTB graft was introduced through the proximal conical formed femoral tunnel, in which the proximal equally conical formed bone block was press fitted and blocked. The distal bone block fixation was done with a 6 × 23 mm bioabsorbable interference screw, made of poly-D,L-lactide (Sysorb; Sulzer Orthopedics, Baar, Switzerland). The patient subsequently did well and returned after 6 months to the same level of activity as before the injury.

Eight months after the operation, however, the patient noted swelling and pain over the anterior proximal tibia. There was no history of a new trauma or of a giving way. A tender, fluctuant mass was palpable over the end of the tibial tunnel and the whole anteromedial proximal tibia showed inflammatory signs. Radiographs revealed a large osteolytic formation at the proximal tibial tunnel (Fig 1).

Figure 1. Anteroposterior radiograph of the left knee showing a large osteolytic formation at the proximal tibial tunnel 1 year after ACL reconstruction with BPTB and tibial fixation with bioabsorbable interference screw.

Click on Image to view full size

Magnetic resonance imaging showed enlargement of the tibial tunnel, which was filled with fluid and communicated with another pretibial subcutaneous fluid-filled cyst (Fig 2).

Figure 2. Sagittal magnetic resonance image showing fluid in the tibial tunnel and extending out of the tibial tunnel forming a subcutaneous cyst.

Click on Image to view full size

The distal bone block of the BPTB graft was integrated in the surrounding bone and the bioabsorbable interference screw could not be identified. There were no signs of effusion or synovial hypertrophy within the knee joint. Examination under anaesthesia revealed only grade 1 Lachman test and negative pivot shift results.

At arthroscopy, the knee joint showed no signs of any intra-articular inflammatory reaction or foreign body evidence. The ACL graft was intact, covered with normal synovia (Fig 3), and manifested a good tension at the arthroscopic-controlled Lachman test.

Figure 3. Arthroscopic view of the intact ACL graft without any inflammatory reaction inside the knee joint.

Click on Image to view full size

Histological examination from the tibial attachment of the ACL did not show any inflammatory or granulomatous reaction.

After open excision of the pretibial cyst, which entered directly into the tibial tunnel, the tunnel was debrided. Inside the tunnel, a remaining part of the head of the bioabsorbable interference screw was found distally (Fig 4) and, proximally, some cystic formation was found inside the bone, filled with a gelatine-like mass.

Figure 4. Arthroscopic view of tibial tunnel showing the remaining head of the bioabsorbable interference screw beside the integrated bone block of the graft.

Click on Image to view full size

There was no connection between the tunnel cavity and the knee joint. Bone grafting was not performed. The histological examination of the cyst wall and the gelatine-like mass did not show any refractile material or inflammatory response. At follow-up 2 months later, the patient was free of symptoms and there was no evidence of recurrence.


Bioabsorbable interference screws composed of poly-lactic acid polymers have been used in ACL surgery for about 5 years with good clinical results.2,5,6,10 It was thought that foreign body as well as giant cell reactions in soft tissue and bone or synovitis in joints that were described after using polydioxanone, polyglycolide and lactide-glycolide polymers would be eliminated.7,8,11 Recently, however, Takizawa et al.9 reported the case of a severe gonitis after screw breakage following intercondylar prominence fracture with poly-L-lactic acid screws. In this case, mechanical irritation of the loosed broken screw seemed to stimulate the foreign body reaction in the joint. Imhoff et al.6 reported lytic changes around the bioabsorbable PLLA screws at the femoral site after ACL reconstruction in two female high-level athletes who underwent very aggressive postoperative rehabilitation.

Subcutaneous pretibial ganglion-like cyst formations similar to the one presented above were also described after ACL reconstruction with soft-tissue allografts and autografts using metal hardware for graft fixation.12,13 In these cases, another mechanism was postulated. Incomplete incorporation of the allograft tissue within the bone tunnels or pressure necrosis of the graft fibers were proposed as explanation for the cyst development.12,13

In our opinion, the tibial bone tunnel enlargement and the tibial subcutaneous cyst in this case report were caused by an adverse reaction of the bone to the bioabsorbable material used. In this case, no substitution of the polymer material took place by osseous neoformation in the tibial tunnel up to 8 months after the ACL reconstruction. ACL reconstruction with autologous BPTB using the press fit technique and distal bone block fixation with the Sysorb bioabsorbable interference screw have been performed in 25 patients among 250 treated with ACL insufficiency since 1996 in our department. The incidence reported here is the first complication involving bioabsorbable screw fixation, resulting in a complication rate of 4% in our series.

We believe that the surgeon should be aware of and be prepared to treat this type of complication. Future clinical studies will show if the advantages of bioabsorbable screws in ACL surgery prevail over their potential complications.

   Publishing and Reprint Information  TOP