Postmeniscectomy osteonecrosis of the knee: A case report and literature review

INTRODUCTION

Osteonecrosis of the knee is the development of an ischemic lesion generally on the weight-bearing surface of the medial femoral condyle.^[1] Osteonecrosis lesions are classified as spontaneous, secondary, or postarthroscopic osteonecrosis of the knee (PAONK), the latter including postmeniscectomy osteonecrosis of the knee (PMONK) and osteonecrosis of the postoperative knee.^[2,3] PMONK has a low incidence of reporting and

On examination, the patient was obese, with a body mass index of 31 kg/m². He had a normal gait pattern, with a full range of motion of the knee joint bilaterally, and no lower extremity muscle weakness. There were no signs of right knee effusion or indication of infection, and ligament stress tests were negative. A mild genu varus alignment was observed bilaterally. On palpation, there was significant tenderness along the medial aspect of the right knee. Radiographs revealed early mild arthritic changes, with mild bilateral narrowing of the medial joint space [Figure 1]. Magnetic resonance imaging (MRI), performed 6 months after symptom onset, revealed a degenerative tear of the medial meniscus, with intact cartilage and no sign of osteonecrosis [Figure 2]. Conservative management was recommended, including weight loss, activity modifications, continued use of NSAIDs, and physical therapy.

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Figure 1:

Preoperative standing radiograph showing mild arthritic changes of the knee joint.

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Figure 2:

(a) Coronal and (b) sagittal preoperative magnetic resonance images of the right knee showing a degenerative medial meniscal tear, with no evidence of osteonecrosis.

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The patient underwent arthroscopic partial medial meniscectomy at another institution in Europe. He returned to our clinic 6 months later due to worsening pain over the previous 3 months. He now reported the pain in the medial knee compartment as sharp and of greater severity than preoperatively, which significantly limited his activities of daily living and required a gait aid. On examination, there was no sign of surgical wound infection. Radiographs revealed a radiolucent cortical bone depression with a rim of bony sclerosis on the medial femoral condyle [Figure 3]. A repeat MRI (6 months after surgery) confirmed the presence of bone marrow edema, associated with irregularity of the articular surface, and an area of depression on the medial femoral condyle [Figure 4]. Conservative treatment, including NSAIDs and a course of non-weight-bearing, was attempted initially. Without improvement after 6 months, we proceeded with total knee arthroplasty (TKA). Intraoperatively, a contained osteochondral defect of the medial femoral condyle extending to the subchondral bone was identified. Because it was a contained and shallow lesion, it was filled with cement only [Figure 5].

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Figure 3:

A standing anteroposterior radiograph showing a radiolucent lesion of the medial femoral condyle with a significant bony depression (crescent sign).

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Figure 4:

(a) Coronal T2- and (b) T1-weighted magnetic resonance images showing a focal subchondral patch of decreased bone marrow signal on the T1-weighted image and a high signal on the T2-weighted image of the medial femoral condyle, which indicate bone marrow edema. Irregularity of the articular surface, with a subtle depression of the articular surface and signal alteration, was observed.

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Figure 5:

(a) Anteroposterior and (b) lateral radiograph showing the knee after TKA.

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DISCUSSION

To our knowledge, this is the first case of PMONK reported from the Middle East and Arab countries. It is currently unclear whether this is secondary to differences in ethnicities or if cases have been underreported.

In this case, the most likely etiology was the meniscectomy. Although the etiology of PMONK remains to be fully elucidated, meniscal tears and meniscectomy are commonly associated factors of spontaneous osteonecrosis of the knee (SONK) and PAONK, respectively.^[2,6-12] Osteonecrosis after meniscectomy may result from a change in load distribution and a resultant increase in tibiofemoral contact force, leading to fissuring and micro-fracturing of the cartilage.^[7] Hussain et al.^[8] identified either meniscal tears or meniscectomy in the development of osteonecrosis of the knee in > 80% of studies, recommending use of the term subchondral insufficiency fractures. Pre-existing cartilage damage or iatrogenic injury during arthroscopy may be other contributing factors allowing leakage of fluid into the subchondral bone during the procedure, which could lead to subchondral edema and, eventually, osteonecrosis.^[7,13,14]

In the current case, the diagnosis of PMONK was made based on preoperative MRI findings of intact cartilage with no sign of osteonecrosis or bone marrow edema 6 months after symptom onset. As the early stages of PMONK primarily affect the subchondral bone and bone marrow, plain radiographs have limited diagnostic value, with MRI being the gold standard. The presence of bone marrow edema observed on preoperative MRI at 4–6 weeks after symptom onset is the main criterion differentiating spontaneous from post-meniscectomy osteonecrosis.^[15] For the diagnosis of post-meniscectomy osteonecrosis, the chronology between the meniscectomy and postoperative MRI evidence of osteonecrosis is important to consider, with a minimum of 3 months after surgery needed to detect the MRI findings of osteonecrosis owing to the large non-specific area of bone marrow edema in the femoral condyle expected immediately after surgery.^[13]

Even though the osteonecrosis size in the current case was small, the prognosis was poor and symptom progression was fast, eventually requiring TKA. Currently, there is no classification system specific to PAONK or PMONK. However, as the clinical features, radiographic findings, and the disease process are similar to those of SONK, the 5-stage radiographic classification for SONK is helpful.^[16] However, while the size of the lesion in SONK affects prognosis and treatment, the size of the PAONK lesion does not correlate with outcome.^[3] In fact, Johnson et al.^[6] reported rapid progression of osteonecrosis in 71% of PAONK cases, which required subsequent surgical intervention 7 months after the arthroscopy.

Currently, there are no consensus or evidence-based guidelines for PMONK treatment. Generally, conservative treatment is recommended as the first step to avoid the potential risk of accelerated joint destruction.^[15] Weight-bearing restriction for 4–8 weeks, in combination with NSAIDs and muscle strengthening, is recommended, followed by a gradual return to activities based on symptoms.^[13] However, in this case, conservative measures failed to relieve patient symptoms or stop disease progression. Therefore, conservative treatment may be less effective for PAONK than SONK, with one study reporting improvement in MRI findings after 6-week protected non-weight-bearing in only 3/47 (6.4%) cases of PAONK.^[13] Bisphosphonates, which promote bone formation by reducing the activity of osteoclasts,^[17,18] have been shown to improve pain after 4–6 weeks and completely resolved symptoms in > 50% of patients at the 6-month follow-up.^[19] In the same study, an 80% decrease in the pain score was reported with administration of intravenous pamidronate over a period of 2 weeks, followed by a weekly oral dose of alendronate for 4–6 months among 28 patients (22 PAONK and 6 SONK).^[19] The use of vasodilators, such as iloprost,^[20,21] and anticoagulants, such as enoxaparin,^[22] have been reported for the treatment of early-stage pre-collapse osteonecrosis, although further research is needed to clarify these effects. Surgical treatment is indicated for patients who do not respond well to at least 3 months of conservative management, have no clinical or radiographic improvements, or have a lesion > 5 cm.^[16,23] Arthroscopic chondroplasty or debridement has a limited role in treating PMONK as it will not modify the natural progression of the pathology, except in cases where mechanical symptoms are present.^[13,24] High tibial osteotomy (HTO) can be considered for active young patients with a varus malalignment and early-stage disease of the medial knee compartment. HTO shifts the weight-bearing axis more laterally, offloading the medial compartment; good outcomes of HTO have been reported for cases of spontaneous osteonecrosis.^[13,25] However, the effectiveness of HTO for PMONK remains to be clarified. Similarly, core decompression has been shown to provide good outcomes for stage I and II spontaneous osteonecrosis, including successful healing in most patients with stage I lesions.^[26,27] Unicompartmental arthroplasty is a viable option for patients with a lesion isolated to a single femoral condyle or tibial plateau involvement, with no significant malalignment. TKA is advised for patients with evidence of contralateral compartment or patellofemoral joint degenerative changes.^[28] In this case, the patient had significant clinical improvement after TKA.

CONCLUSION

The incidence of PMONK has not been clearly defined in the Middle East and Arab countries. Our case indicates that PMONK does occur in these areas; thus, surgeons should be aware of this possibility. In the absence of consensus and evidence-based guidelines, treatment should be based on presenting symptoms, functional limitations, and best available evidence.

AUTHOR’S CONTRIBUTION

The author has critically reviewed and approved the final draft and is responsible for the manuscript’s content and similarity index.