What did the study look at?
One of the grafts used in anterior cruciate ligament (ACL) reconstruction is the quadriceps tendon (QT), the tendon of the muscle group at the front of the thigh. It is sometimes harvested together with a small block of bone from the kneecap (patella). The authors note that kneecap fractures can occur after a bone block is taken, at rates of up to 8.8% in one study. Because the longest part of the tendon does not always lie over the centre of the kneecap, the bone block may sometimes be taken further towards the outer side.
The aim of this study was to define how thick the remaining kneecap bone is across the graft harvest site and to provide guidance on harvesting the bone block safely.
How was it done?
This is a cadaveric study carried out on 13 kneecaps donated for medical research; the bone block harvest was simulated on computer.
- The longest part of the tendon was identified and a graft area 10 mm wide and 20 mm long was marked on the kneecap accordingly.
- Three-dimensional models of the kneecaps were created from computed tomography (CT) images.
- A virtual bone block with a maximum depth of 10 mm was removed and the remaining bone thickness was measured in 9 zones.
- Zones with less than 50% of the total kneecap depth remaining were defined as "risk zones" for fracture.
What did it find?
- Harvest location varied considerably: the outer edge of the graft area lay between 21.2% and 49.2% of the kneecap width from its outer border.
- Significantly less bone remained in the outer column of the harvest site (mean 7.56 ± 2.19 mm) than in the inner column (9.83 ± 2.10 mm) (P = .028).
- 77% of kneecaps (10 of 13) had at least one risk zone, most often in the upper-outer and central-outer zones.
- For every 1 mm closer the graft edge was to the outer border of the kneecap, the number of risk zones rose by 0.59; for every 1 mm further away, the remaining bone in the outer column was 0.412 mm thicker.
- In kneecaps without risk zones, the outer edge of the graft lay a mean of 18.9 mm (43% of the width) from the outer border, compared with 12.5 mm (30.5%) in those with at least one risk zone.
The authors' conclusion
According to the authors, harvesting the quadriceps tendon bone block from further towards the outer side of the kneecap leaves thinner bone behind and increases the chance of encountering a risk zone for fracture. They state that care should be taken to avoid harvesting the bone block too far to the outer side during surgery.
Limitations
- The bone block harvest was virtual; in real surgery, surgeons' measurements and cutting angles may differ.
- Anatomical measurements were made by a single investigator, so reliability could not be tested.
- Tendon length was not measured, and the age, height, weight and sex of the specimens were not available.
- Whether the thinner bone actually leads to fracture was not tested biomechanically; further research is needed.
Reference
Perry AK, Dandu N, Knapik DM, Inoue N, Gürsoy S, Bush-Joseph CA, Yanke AB, Chahla J. Lateral Harvest of an Osseous-Based Quadriceps Tendon Autograft Results in Thinner Remaining Patellar Bone. Orthopaedic Journal of Sports Medicine. 2022;10(5):23259671221093685. Licence: CC BY-NC-ND 4.0.
DOI: 10.1177/23259671221093685
Free full text: PubMed Central (PMC9083045)
This article summarises a published scientific paper for general information; it does not replace an examination or a personal medical assessment. Please consult your doctor about your symptoms.
