- Discussion:
- 2 subtypes: rim avulsions and rim compression frx;
- all knees w/ rim frxs have capsular and collateral ligament injuries;
- avulsions of rim of tibial plateau articular surface or compression
frx of that rim almost always are accompanied by significant
collateral or cruciate ligament injury;
- may represent fracture dislocation;
- Radiographs:
- diagnostic studies of these fractures should include x-rays obtained
w/ knee in genu valgus and genu varus stress;
- diagnosis ismade on anteroposterior x-rays that show a rim compression
frx and/or a rim avulsion fracture;
- Rim Avulsion Fracture:
- comprimising 16% of frx dislocations of the Fracture Dislocations;
- occurs w/ severe valgus or varus forces exerted on joint capsule & collateral
ligaments creating ligament injury along w/ fragment of articular margin;
- this type almost exculsively involves lateral tibial plateau, w/
avulsion frags of capsule attachment, Gerdy's tubercle, or plateau;
- disruption of either or both cruciate ligaments is common;
- menical injury is rare;
- neurovascular injuries occur in 30% of frxs, & nearly all type III frx are unstable;
- Lateral approach allows screw fixation of the articular rim and repair
of avulsed iliotibial band & collateral ligaments;
- Rim Compression Fracture:
- this injury accounts for about 12% of all Fracture Dislocations;
- it is almost always unstable;
- opposite collateral ligament complex & cruciate ligaments are usually
avulsed or torn, allowing the tibia to sublux which causes a secondary
compression frx of a portion of anterior, posterior, or middle articular rim;
- Non Operative Treatment:
- indicated if rim compression is small & knee shows < 10 deg of instability;
- frx brace, cast brace, or long leg cast provides sufficient support
during the 6 to 8 weeks required for soft tissue healing;
- Operative Treatment:
- PreOp Planning
- is used in knees w/ > 10 deg of instability with avulsion frxs, or with large rim
compression fractures;
- parapatellar approach allows debridement of small fragments, elevation and
stabilization of the larger fragments, & repair of cruciate and opposite
collateral ligaments;
- rim compression frxs are elevated thru smal incision made just below joint line;
- articular surface and the fracture are visualized thru the infra-meniscal interval;
- small coritcal window is made distal to the rim fracture & depressed articular
margin is elevate to normal position w/ osteotome or elevator;
- local cancellous grafts are used to fill the resulting defect;
- if there is rim avulsion frx on opposite side of knee, it is repaired and fixed in
its bed by a screw;
- Post Operative Care and Compications:
- cast brace is used for 6 weeks;
- wt bearing is delayed for 8 weeks to allow consolidation of frx and
healing of repaired capsular & collateral ligaments;
- loss of screw or pin fixation is main complication of rim frx;
- late problem noted most often is knee instability;
