Title: Cogwheel Grooves on Patellofemoral Articular Surfaces in a Cadaver
Authors: Schafer Paladichuk, OMS1; Alex Gonzaga, OMS1; Jonathan Lindsey, OMS1; Ronald Walser, DPT
Introduction
The presence of multiple longitudinal, parallel grooves on lateral femoral condyles with matching grooves on articular surfaces of patellae is an odd occurrence, and few cases have been reported. In one report, these grooves were described as cogwheel grooves. The purpose of this case report is to describe the abnormal occurrence of bilateral longitudinal grooves, or cogwheel grooves, found in the knees of a cadaver.
Case Description
Bilateral knees of a 98-year-old female donated body were examined. To obtain an appropriate view of the articular surfaces and take measurements of the internal aspects of bilateral knees, the quadriceps tendons were severed, and the patellae were reflected inferiorly. Both femoral heads were dislocated to measure femoral length from the head of the femur to the distal end of the medial condyle. Tibias were also measured from tibial plateau to the talocrural joint.
Longitudinal grooves were observed bilaterally on the lateral femoral condyles and the articular surfaces of patellae. Photos were taken of bilateral femoral condyles and patellae to show the cogwheel grooves within bilateral patellofemoral joints. No grooves were seen within the hip or talocrural joints. A slight bilateral genu valgum was apparent. The right femur length was 423 mm, and the left femur length was 419 mm. There was a hip replacement on the left side. The left tibial length was 343 mm, and the right tibial length was 345 mm. The cogwheel grooves were more prominent within the left knee, as compared to the right knee. The cogwheel grooves were well isolated to the lateral femoral condyles and the near entirety of the articular surface of the patellae, bilaterally.
Discussion
The occurrence of cogwheel grooves on the lateral femoral condyles and articular surfaces of patellae appears to be relatively uncommon. The lack of medical history and demographic information on this cadaver limits the ability to infer potential causes of the cogwheel grooves. Cause considerations could include, but should not be limited to, osteopathia striata, osteochondritis dissecans, and osteoarthritis. An increased Q-angle could possibly contribute to advanced osteoarthritis, causing grooves in the knees, specifically between the lateral femoral condyles and the patellae. It is not certain whether these cogwheel grooves are the result of pathology or consequence of aging. Future studies could include a retrospective review of imaging studies, linking medical history and demographic information to cases of cogwheel grooves found in knees.
I am one of the judges for this interesting case presentation. You mentioned several possibilities about what could have created these grooves, but there was nothing definitive. In what you have read about cogwheel grooves as well as what you know about this cadaver, if you had to bet, what do you think caused it and why do you think that?
Dr. Callahan, thank you for your question. My research team and I spent a lot of time going back and forth on this topic. Of the potential etiologies we listed, Osteopathia Striata, Osteochondritis dissecans, and Osteoarthritis, we believe this presentation points towards a case of Advanced Osteoarthritis due to a lateral tracking of the patella.
With the increased Q angle observed, the left side being more prominent due to a hip replacement, we believe the increased lateral traction of the patella resulted in the osteoarthritic eburnation of the lateral femoral condyles and dorsal surface of the patellae. Increased lateral traction of the patellae would have created poor patella tracking whenever the patellofemoral joint was in motion. This poor traction over the years may have resulted in the symmetrical longitudinal grooves we observed.
We came across one article, “Ridges and grooves on bony surfaces of osteoarthritic joints,” by Rogers and Dieppe, describing this presentation; however, that was the only similar presentation we found documented. It is likely that biomechanical changes in addition to some sort of congenital deficit or some other cause may have contributed to these abnormalities; however, we cannot infer this as we do not have access to the cadavers past medical history.
Thank you again for this question and taking to time to review our case report!
PA;, R. J. M. D. (n.d.). Ridges and grooves on the bony surfaces of osteoarthritic joints. Osteoarthritis and cartilage.
Retrieved December 28, 2021, from https://pubmed.ncbi.nlm.nih.gov/15449422/
One of the Judges: Can you do a differential diagnosis including the possible pathological/inflammatory processes for the possible causes of these bilateral cogwheel grooves and explain why you ruled out each alternative and proposed genu vulgum as a possible cause?
Dr. Novack, thank you for your question. Our working diagnosis for this presentation is Advanced Osteoarthritis due to lateral tracking of the patella. The differential diagnosis we came up with includes Osteopathia Striata and Osteochondritis dissecans. For this case report, we could only base our possible cause of genu vulgum off presentation as we were unable to gain access to the cadavers’ past medical history.
Osteopathia Striata is characterized by striations at the sites of endochondral bone formation. This pathology is an asymptomatic autosomal dominant disorder commonly seen around the metaphysis of long bones or at the base of the cranium. This condition predominates in females and occurs with a non-functioning AMER1 gene. The AMER1 gene provides instructions for making proteins that aid in the Wnt signaling pathway. A disruption in this process results in sclerosis at the ends of long bones, head, face, increased head size, and a cleft palate. We decided to rule this pathology out as the cadaver did not present with any additional abnormalities associated with the head or face. Additionally, radiographic findings related to Osteopathia Striata were not consistent with the presentation of the cadaver. The striations seen in the radiographic images of Osteopathia Striata were commonly observed more towards the metaphysis of the femur and were more commonly associated with the skull and face.
Our other differential, Osteochondritis dissecans, is characterized by lesions of the subchondral bone within the knee. These lesions are pathological, affecting the articular cartilage and subchondral bone with variable clinical patterns. The mechanisms of this pathology usually come about in one of three ways, hereditary, traumatic, or vascular. All three pathological causations result in softening the articular cartilage, cartilage separation, and potential detachment of the lesion (joint mice). The latter of pathological causations was our first reason to rule this out as a possible diagnosis; when we opened the patellofemoral joint bilaterally, no loose bodies or lesion detachments were seen on the lateral femoral condyles and dorsal surfaces of the patellae. Additionally, Osteochondritis dissecans are commonly seen radiographically with random presentations; the cogwheel grooves seen in this cadaver were symmetrical bilaterally was another reason we do not believe this is a case of Osteochondritis dissecans.
Thank you again for your question and time, Dr. Novack.
Judge: This is an interesting case. You mention that a lack of demographic information limits the ability to infer potential causes of the cogwheel groves. What additional hypotheses have you considered to connect certain demographic information as a possible cause?
Hi Jennifer, great question. Our research team pondered this exact question trying to come up with any conclusions that could lead us to this interesting presentation. We know a few demographics from observation and the limited information on the cadaver: the age was 93, and the gender was a female. Age is a strong factor contributing to osteoarthritis as it is considered “wear and tear” some would argue that if you live long enough, some type of arthritis is almost guaranteed. Additionally, females tend to have a higher prevalence of osteoarthritis later in life, so both age and gender made us lean toward advanced osteoarthritis.
Since we do not have access to any past medical history for this cadaver, we cannot infer any potential chronic diseases, congenital defects, or genetic abnormalities. One medical operation we do know about is the left hip replacement. We believe this is why the cogwheel grooves are more prominent on the left side, but we also know since the cogwheel grooves are bilateral, they would have been present before the total hip replacement.
Some additional hypotheses we considered revolved around congenital defects or genetic abnormalities. We believe this case of suspected advanced osteoarthritis results from poor biomechanics that caused lateral tracking of the patellae and, consequently, cogwheel grooves. The poor biomechanics could result from conditions such as Marfan’s or Ehlers-Danlos’s syndrome. The laxity in the joint connective tissue and weakened muscles could have also resulted in the poor tracking of the patellofemoral joint. Another potential hypothesis is this cadaver was simply born with these cogwheel grooves, and over time they may have become more pronounced. Finally, if we had more medical history on race, ethnicity, and occupation, we would have also been able to infer more. Specific populations such as Asians have a higher prevalence of osteoarthritis in the knees specifically, and specific occupations that require more intense labor have a higher rate of people suffering from osteoarthritis.
I hope this answers your question, Jennifer; again, thank you for your time in reviewing our case report.