Congenital absence of the lateral meniscus: A case report

Abstract

BACKGROUND

Congenital absence of the menisci is a rare anatomical variation characterized by the absence or underdevelopment of one or both menisci in the knee joint. The menisci are crucial in load distribution, joint stability, and shock absorption. Understanding the clinical presentation, diagnosis, and management of this condition is important for optimal patient care.

CASE SUMMARY

A 27-year-old male with a long-standing history of knee pain underwent diagnostic arthroscopy, revealing a congenital absence of the meniscus. The patient's clinical findings, imaging results, surgical procedures, and pertinent images are detailed. This case presents a unique aspect with the congenital absence of the meniscus, contributing valuable insights to the literature on rare anatomical anomalies.

CONCLUSION

This case of congenital absence of the menisci highlights the diagnostic challenges posed by rare anomalies. The diagnostic arthroscopy played a crucial role in identifying the absence of the meniscus and providing an explanation for the patient's persistent knee pain. The case underscores the importance of individualized treatment approaches, including physical therapy, for optimal management of rare meniscal anomalies. Further research is warranted to explore effective management strategies for the aforementioned cases and to expand our knowledge of these rare conditions.

Key Words: Lateral meniscus; Arthroscopy; Knee joint; Menisci reformation; Magnetic resonance imaging; Case report

Core Tip: Congenital absence of the menisci is a rare anatomical variation characterized by the absence or underdevelopment of one or both menisci in the knee joint. We present a young male patient with a long-standing history of knee pain who underwent diagnostic arthroscopy, revealing the congenital absence of the lateral meniscus. The patient's clinical findings, imaging results, and surgical procedure are presented, along with relevant images. This case is notable for the congenital absence of the meniscus, a finding that contributes to the literature on such rare anomalies.

INTRODUCTION

Congenital absence of the menisci represents a rare anatomical variation where one or both menisci are absent or underdeveloped in the knee joint[1]. The menisci, comprised of fibrocartilaginous tissue, play a vital role in load distribution, joint stability, and shock absorption within the knee[2]. The absence of these structures can have significant implications for knee function and may lead to symptoms such as pain, instability, and limited range of motion. This literature review aims to provide an overview of the current understanding of congenital absence of the menisci, including the etiology of the condition, clinical presentation, diagnostic methods, and management strategies.

Clinically, patients diagnosed with congenital absence of the menisci often present with knee pain, instability, and limited range of motion. The absence of these significant structures compromises the load-bearing capacity of the knee joint, leading to altered biomechanics and increased stress on the articular surfaces[3]. In some cases, patients may experience mechanical symptoms such as catching, clicking, or locking of the knee.

Diagnosing congenital absence of the menisci can be challenging, as the condition may remain unnoticed until symptoms manifest. Physical examination may reveal a limited range of motion, joint line tenderness, or instability. Imaging modalities such as radiographs (X-rays), magnetic resonance imaging (MRI), or arthroscopy can aid in confirming the absence or underdevelopment of the menisci and assessing associated structural changes.

Management strategies for congenital absence of the menisci depend on the severity of symptoms and associated findings. Non-operative approaches, including physical therapy, analgesic medications, and activity modification, may initially alleviate pain and improve knee function[4]. However, in cases where symptoms persist or significant structural abnormalities are present, surgical intervention may be necessary.

Surgical options range from meniscal repair or transplantation to partial or total meniscectomy. The choice of procedure depends on the extent of meniscal absence or abnormality and the preservation of other knee structures. Moreover, individualizing the treatment approach based on each patient's unique presentation and goals is necessary. In cases where meniscal preservation is not feasible, the focus shifts towards optimizing joint function and preventing further degeneration. Ongoing monitoring and management of associated findings, such as cartilage damage or joint instability, are essential in maintaining long-term knee health.

CASE PRESENTATION

Chief complaints

A 27-year-old male with no significant medical history presented with a complaint of left knee pain that started 15 years ago.

History of present illness

The patient first experienced pain in his left knee during childhood, and it has been intermittent ever since, localized to his left knee without involvement of any other joints. The pain progressively aggravated with activity and improved with rest. The patient reported no recent history of trauma to the knee and denied any catching or giving way sensation. However, he did mention experiencing clicking sounds during knee movements. Furthermore, no accompanying symptoms such as fever, night sweats, weight loss, or loss of appetite were observed. Over the past year, the pain has become constant, even without any recent traumatic event.

History of past illness

The patient recalled experiencing similar symptoms when he was 12 years old, including catching and clicking sensations in the knee and an inability to fully flex it. At that time, the symptoms improved with time and physical therapy. The patient had no known allergies and was not ingesting any analgesic medications. He had undergone physical therapy on multiple occasions, which had provided some improvement in his symptoms.

Personal and family history

The patient had no significant past medical, surgical, or family history.

Physical examination

Upon examination, no visible swelling, erythema, or signs of infection were observed around the knee. The contour of the knee appeared normal, with no tenderness along the joint line. Palpation of the knee elicited neither pain nor discomfort. Range of motion was not limited, with extension measuring -5° up to 130° flexion. Tests performed, including the Lachmann test, anterior drawer test, and posterior drawer test, yielded negative results. No sag sign was observed, and the valgus and varus tests demonstrated stability. The dial test and grinding test were also negative. Furthermore, X-ray imaging displayed no signs of arthritis or widening of the joint line.

Laboratory examinations

No abnormalities were revealed in the laboratory examinations.

Imaging examinations

Plain X-ray imaging of the left knee joint demonstrated normal visualized bone densities with no evidence of fracture or dislocation (Figure 1A). The joint spaces were preserved, and the soft tissues appeared unremarkable, as displayed in Figure 1B. MRI of the patient confirmed that the anterior and posterior cruciate ligaments were intact. Significant attenuation and abnormal morphology of the posterior aspect of the body and posterior horn of the lateral meniscus were observed, along with thickening of the anterior meniscal tissue. The integrity of the medial meniscus was preserved. The collateral ligaments and extensor mechanisms were intact, with no evidence of joint effusion. A small popliteal cyst was observed. Furthermore, focal deep cartilage fissuring was noted at the posterior aspect of the lateral femoral condyle (Figure 2).

Figure 1 Plain radiography of the left knee displays preserved joint spaces with no fractures or dislocations. A: Plain anteroposterior radiography; B: Plain lateral radiography.

Figure 2  Coronal, axial, and sagittal T2-weighted magnetic resonance imaging of the left knee demonstrates intact cruciate ligaments and medial meniscus.

FINAL DIAGNOSIS

Based on the history, physical examination, imaging, and diagnostic arthroscopy, the patient was diagnosed with congenital absence of the lateral meniscus.

TREATMENT

During the diagnostic arthroscopy, the absence of the lateral meniscus was discovered in the patient (Figure 3). No other surgical intervention was required. The patient continued with a range of motion and strengthening physical therapy for six months.

Figure 3  Arthroscopic views of the left knee display a congenital absence of the lateral meniscus.

OUTCOME AND FOLLOW-UP

Clinically, the patient demonstrated improvement on a one-year follow-up with a pain score of zero and an Oxford knee score of 48.

DISCUSSION

The meniscus, one of the contributors to knee stability, is composed of fibrous cartilage[5]. The characteristic meniscus shape is formed by the eighth week of gestation when the knee is fully formed. The lateral femoral condyle is located at a high position with significant lateral long-axis deviation. The lateral tibial plateau is more circular than the medial tibial plateau. This normal anatomical variation causes asymmetric knee movement. The lateral meniscus shape, which is more widely variable than the medial meniscus, seems to adapt to the asymmetric knee motion. Such morphological variation could be involved in lateral meniscus anomalies[6].

The presented case is of a 27-year-old male with a long history of knee pain, tracing back to childhood, without any significant traumatic events. One striking finding is the congenital absence of the meniscus, discovered during diagnostic arthroscopy. This finding aligns with the rare occurrence of congenital meniscal anomalies as discussed in the initial literature.

The anomalies typically affect the lateral side of the knee, as supported by the significant attenuation of the posterior aspect of the body and posterior horn of the lateral meniscus in this patient. Contrary to Sachleben et al's[7] findings, no notable abnormalities were identified in the patient's articular surfaces or cruciate ligaments.

In the discussed literature, it is mentioned that the absence of the meniscus should lead to some degree of wear on the articular surfaces. This aligns with the finding of focal deep cartilage fissuring at the posterior aspect of the lateral femoral condyle in our patient, suggesting a certain level of cartilage damage despite the absence of typical signs of arthritis on the X-ray[7].

A unique aspect of this case is the congenital absence of the meniscus, which adds valuable insights to the literature on this uncommon anomaly. Although meniscal hypoplasia has previously been reported, isolated bilateral hypoplasia of the medial meniscus remains a first, as per available knowledge[8]. The case also emphasizes the importance of exploring the cause of knee pain via diagnostic arthroscopy, especially when symptoms persist despite conservative treatments like physical therapy.

Generally, lateral knee anomalies commonly involve a discoid meniscus, with only a few described cases of bilateral lateral meniscus hypoplasia and partial deficiency[9].

Finally, the natural history of these anomalies and their effect on normal knee function remains unclear. The patient's significant improvement post-arthroscopy and physical therapy is encouraging. The improvement suggests that even with rare meniscal anomalies, adequate diagnosis and management can lead to favorable clinical outcomes, including the reduction of pain and improvement of function.

CONCLUSION

In summary, this case presentation contributes to our understanding of congenital meniscal anomalies, particularly the rare occurrence of the absence of the lateral meniscus. Diagnostic arthroscopy played a crucial role in uncovering the congenital absence of the meniscus and identifying associated structural changes. The successful management of the patient's symptoms through physical therapy underscores the significance of individualized treatment approaches. In the future, delving deep into the management strategies for such rare anomalies. This will help improve patient outcomes and optimize the care of individuals with congenital meniscal anomalies.