Subchondral Insufficiency Fracture of the Knee: A Hidden Culprit of Joint Pain in Elderly Women

 Subchondral Insufficiency Fracture of the Knee: A Hidden Culprit of Joint Pain in Elderly Women

Introduction

Knee pain in elderly individuals is often attributed to degenerative joint disease, such as osteoarthritis. However, when the pain is sudden, severe, and worsened by weight-bearing, particularly in older women without significant trauma history, a more elusive diagnosis must be considered: Subchondral Insufficiency Fracture (SIF).

In this article, we present a case of SIF in a 66-year-old woman, utilizing multimodal imaging, and provide an in-depth review of its clinical implications, MRI findings, differential diagnosis, treatment options, and prognosis.

---

Case Summary

Patient: 66-year-old female

Chief complaint: Acute knee pain after minor twisting injury

Pain: Sharp, worsened by movement and weight-bearing

Imaging: Plain radiographs and MRI

Radiographic Findings

Subtle sclerosis in the medial femoral condyle

No clear fracture line or collapse

Mild joint effusion

Radiographs were inconclusive, prompting further imaging with MRI.

MRI Findings

Curvilinear hypointense line along the subchondral surface of the medial femoral condyle (low signal on T1 and PD-FS)

Extensive surrounding bone marrow edema

Subchondral fluid-filled cleft indicating possible cortical collapse

Full-thickness cartilage loss

Extrusion of the medial meniscus

Subchondral fracture was also noted in the medial tibial plateau

Partial tear of the medial collateral ligament (MCL)

---

Quiz

1. Which component has a subtle finding that may require further workup?

(A) Inferior patellar border

(B) Medial femoral condyle

(C) Medial femoral epicondyle

(D) Tibial tuberosity

(E) Quadriceps tendon

Explanation: Subtle sclerosis in the medial femoral condyle may suggest a subchondral insufficiency fracture. Further MRI workup is warranted if symptoms are severe.

 

2. There is a curvilinear low signal along the subchondral medial femoral condyle.

(A) TRUE

(B) FALSE

Explanation: This finding is classic for subchondral fracture—a low-signal intensity line representing cortical discontinuity.

3. Which of the following is a poor prognostic indicator in subchondral insufficiency fracture?

(A) Extensive bone marrow edema

(B) Medial meniscus extrusion

(C) Subchondral hypointense line > 1 cm

(D) Subchondral fluid-filled cleft

(E) All of the above

Explanation: A longer hypointense line, extrusion of meniscus, and subchondral fluid cleft all suggest subchondral plate collapse, which correlates with poor prognosis.

Discussion

Cause & Etiology

Subchondral insufficiency fracture (SIF) occurs when normal mechanical stress exceeds the structural integrity of osteopenic or osteoporotic subchondral bone. It is more common in elderly women, often without trauma.

Key risk factors: Osteoporosis, advanced age, varus/valgus alignment, repetitive microtrauma, post-menopausal bone loss.

Pathophysiology

Weight-bearing causes microfractures in the subchondral plate.

Inadequate repair → collapse of the subchondral bone

Joint surface becomes unstable → leads to cartilage degeneration

In chronic stages, it may mimic or evolve into osteoarthritis or osteonecrosis

Epidemiology

More prevalent in women > 60 years

Often underdiagnosed due to nonspecific radiographic findings

May coexist with meniscal extrusion or partial MCL injuries

Imaging Features

Modality	Key Findings
X-ray	Often normal or subtle sclerosis
MRI

Curvilinear hypointense subchondral line

Bone marrow edema

Cartilage loss

Meniscal extrusion

Joint effusion

Subchondral fluid cleft

Possible secondary tibial plateau involvement

Differential Diagnosis

Osteochondral impaction fracture

Avascular necrosis (AVN)

Transient bone marrow edema syndrome

Osteoarthritis

Meniscal root tears

Key distinction: SIF presents with acute pain and MRI evidence of subchondral fracture without systemic bone infarction, differentiating it from AVN.

Treatment

Conservative management (if early-stage):

Non-weight-bearing with crutches

NSAIDs

Bisphosphonates (controversial)

Physical therapy

Surgical management (if collapse or non-responsive):

Core decompression

Subchondroplasty

High tibial osteotomy (HTO)

Partial or total knee arthroplasty (TKA)

---

Prognosis

Early diagnosis is key to preventing joint collapse

Lesions with fluid-filled clefts or >1 cm fracture lines are associated with poor outcomes

Meniscal extrusion and full-thickness cartilage loss worsen prognosis

Progression to osteoarthritis is common if untreated

Conclusion

Subchondral insufficiency fracture is an under-recognized but significant cause of knee pain, especially in elderly women. Careful clinical suspicion and MRI interpretation are crucial for distinguishing SIF from arthritis or osteonecrosis. Early diagnosis can change the trajectory of care, preventing irreversible joint collapse and disability.

References

[1] R. Yamamoto and M. Bullough, "Osteonecrosis: Diagnosis and management," J. Bone Joint Surg. Am., vol. 82, no. 3, pp. 377–387, Mar. 2000.

[2] T. Chiba et al., "Subchondral insufficiency fracture of the femoral head," Clin Orthop Relat Res., vol. 399, pp. 145–153, 2002.

[3] A. T. Carrino et al., "MRI of subchondral insufficiency fractures of the knee," Radiology, vol. 237, no. 3, pp. 998–1007, Dec. 2005.

[4] H. Yamagami et al., "Subchondral insufficiency fracture of the knee: Imaging features and treatment outcomes," Radiographics, vol. 33, no. 1, pp. 139–155, Jan. 2013.

[5] E. A. Schweitzer, "MRI of knee cartilage and subchondral bone: Pathologies and pitfalls," Am J Roentgenol, vol. 200, no. 3, pp. 555–564, Mar. 2013.