The hip

Comparison of Hip and Shoulder Joint Stability and Mobility

• Joint Types: Both the hip and shoulder are ball and socket joints.
• Mobility vs. Stability Functions:
  • Shoulder Joint: Specifically built for mobility first and stability second.
  • Hip Joint: Specifically built for stability first and mobility second.
  • Clinical Implications: Because the shoulder prioritizes mobility, shoulder dislocations are significantly more common than hip dislocations. Hip dislocations are generally rare.
• Primary Hip Ligaments: Stability in the hip is provided by three main ligaments:
  • Iliophemoral ligament.
  • Pubofemoral ligament.
  • Ischiofemoral ligament.
• Internal Anatomy: The ligamentum teres is an internal ligament providing stability inside the joint and is notable for carrying a portion of the blood supply to the area.

Hip Musculature and Movements

• Hip Flexors: Prime movers include:
  • Gluteus Medius (anterior fibers).
  • Rectus femoris.
  • Sartorius.
  • Tensor fasciae latae ($TFL$).
  • Iliopsoas.
• Hip Extensors: Prime movers include:
  • Gluteus maximus (the largest and most particular extensor).
  • Hamstrings (noted as highly important hip extensors often overlooked).
• Hip Adductors: Components include:
  • Adductor longus, brevis, and magnus.
  • Gracilis.
  • Pectineus (highly important for adduction).
• External Rotators: Includes various short rotators, the Piriformis, and the Gluteus maximus.
• Internal Rotation:
  • There is no prime mover for hip internal rotation; no single muscle performs only internal rotation.
  • Movement is driven by anterior fibers of the gluteus medius, gluteus minimus, adductor longus, adductor brevis, adductor magnus, and pectineus.

Pelvic Movements and Postural Alignment

• Anterior Pelvic Tilt:
  • Defined by the $ASIS$ moving anteriorly and inferiorly.
  • Results in an increase in lumbar lordosis.
  • Clinically associated with shortened iliopsoas muscles pulling the pelvis anteriorly.
  • Associated with hip flexion and increased lumbar extension.
  • Often described as a "sway back" posture.
• Posterior Pelvic Tilt:
  • Defined by the $PSIS$ moving posteriorly and inferiorly.
  • Results in an increase in hip extension and lumbar flexion.
  • Clinically less common than anterior pelvic tilt.
• Lateral Pelvic Tilt:
  • Occurs in the frontal plane of motion.
  • Defined by the movement of the iliac crest on the contralateral side (opposite of the weight-bearing leg).
  • Elevation: Referred to as "hip hiking."
  • Depression (Drop): Referred to as a Trendelenburg position or Trendelenburg gait (indicative of weak posterior fibers of the gluteus medius).

Kinetic Chain and Weight-Bearing Relationships

• Ripple Effect Analogy: Like a chain hanging from a ceiling, movement at the bottom (foot/ankle) ripples up through the knee and hip. Movement from the top (hip/ladder) ripples down.
• Closed Chain Flexion: When flexing the hip in weight-bearing, it is usually accompanied by knee flexion and ankle dorsiflexion to maintain the center of gravity. This is controlled by the eccentric contraction of hip extensors, knee extensors, and plantar flexors.
• Closed Chain Extension: Standing and moving into hip extension typically causes the knees to lock into extension.
• Hip Adduction in Weight-Bearing: Often manifests as a hip drop (Trendelenburg) on the non-weight-bearing side, usually due to weakness in the hip abductors. This is compared to how models walk.
• Rotational Kinetic Chain: Rotating the trunk while feet are fixed affects foot mechanics:
  • Rotating right causes the right foot to supinate and the left foot to pronate (arch collapsing).
  • Correcting foot position with arch supports can sometimes correct hip rotation issues.

Pathomechanics and Muscle Imbalances

• Muscle Tightness: Common tightness sites include:
  • Quads: Specifically the Rectus femoris; the vastus medialis, intermedius, and lateralis are rarely tight.
  • Hamstrings and Piriformis: Very common.
  • IT Band: Absolutely common.
  • Adductors and Glutes: Less common to be tight.
• Hip Joint Hypomobility: Becomes more common with aging or absence of congenital issues.
• Muscle Weakness and Imbalances:
  • TFL Dominance: The $TFL$ often overpowers the Gluteus medius (specifically the posterior fibers). Clinically, $50\%$ of patients cannot hold the testing position for the posterior glute med (abduction, extension, external rotation) without the leg dropping or rotating.
  • Sartorius Dominance: Overuse of specific quad muscles for hip flexion.
  • Hamstring Dominance: Hamstrings taking over for the Gluteus maximus during hip extension.
  • Lateral Trunk Muscles: Used as compensators for weak hip abductors, causing a side-leaning gait to displace the center of gravity.

Diagnostic Criteria and Clinical Prediction Rules (CPR)

• CPR for Hip Osteoarthritis (OA):
  1. Hip pain (often groin pain).
  2. Internal rotation $< 25^{\circ}$.
  3. Pain with active hip extension.
  4. Pain with active hip flexion (often lateral joint pain).
  5. Positive Scour Test (scouring the ball inside the acetabulum to reproduce pain or grinding).
  6. Pain with squatting.
• Probability Scores:
  • 3 out of 5 symptoms: $29\%$ to $68\%$ probability of OA.
  • 4 out of 5 symptoms: $91\%$ probability of OA.
• Referral Patterns: Hip pain often presents as groin pain or medial knee pain (a common referral pattern).
• Capsular Pattern of the Hip: The order of motion loss is: Internal Rotation > Extension > Abduction > Flexion.

Joint Hypomobility Management

• Activity Limitations: Progressive decrease in tolerance for recreational activities (basketball, etc.), followed by daily activities (standing, stairs, putting on pants).
• Clinical Indicators: Stiffness after rest (warming up after 15–20 steps), hip pain at night, and loss of sleep (the primary driver for seeking care).
• Gait Mechanics: Normal gait requires $40^{\circ}$ of hip flexion, $10^{\circ}$ of hip extension, and $5^{\circ}$ of pelvic rotation.
• Phases of Protection:
  • Maximal Protection Phase: Pain management (ice, medication, joint mobilization), patient education, passive/active-assist range of motion, and aquatic therapy. Note: Aquatic therapy at the navel is $50\%$ weightless, sternum is $75\%$ weightless, and neck is $90\%$ weightless.
  • Moderate Protection Phase: Progressive joint mobility, stretching, mobilization with movement, and aerobic capacity (stationary cycling).
  • Minimal Protection Phase: Progress to isotonic, closed kinetic chain exercises, balance, and functional return-to-activity progressions.

Surgical Interventions

• Arthroscopic Procedures: Included are chondroplasty, microfracture surgery (manages cartilage loss before replacement), and resection of labral tears.
• Structural Reshaping: Rim trimming or osteoplasty to reshapes the bone to decrease impingement.
• Capsular Procedures: Capsular shifts or modifications to loosen a tight capsule or tighten a loose one.
• Total Hip Arthroplasty (THA):
  • Indications: Severe pain, loss of function, joint degeneration (OA/RA), non-union fractures, or bone tumors.
  • Hardware: Titanium is the most common metal. Joints can be Cemented (instantaneous stability, weight-bearing as tolerated) or Cementless (uses coating for bone ingrowth, may require weight-bearing restrictions).
  • Cost/Bundling: THA is often a bundled service (e.g., $\$66,000$ flat fee across 90 days).

THA Surgical Approaches and Precautions

• Posterior Lateral Approach: Incision between glute max and med. Fastest early recovery but highest dislocation risk.
  • Precautions: No flexion $> 90^{\circ}$, no adduction past neutral, no internal rotation.
• Lateral/Antero-lateral Approach: Through the $TFL$ and gluteals. Decreased risk of dislocation but may cause gait asymmetry and muscle weakness.
• Anterior Approach: Incision distal to the $ASIS$, medial to the $TFL$. Low dislocation risk but the most difficult to perform.
• Minimally Invasive: Modification of other approaches with smaller incisions and more muscle sparing.
• Global Trends: Surgical equipment is often on 10-year leases; older equipment is often sold to other countries (e.g., France, Spain).

Post-Operative Complications and Risks

• Intraoperative: Malpositioned prosthetics (rotational problems), additional bone fractures during pounding, leg length discrepancies, and nerve damage.
• Early Post-Operative:
  • Infection: Signs include fever, not feeling well, or redness/warmth (even under waterproof bandages).
  • Deep Vein Thrombosis (DVT): Signs include calf pain, redness, swelling, and severe tenderness when touched.
  • Other: Pneumonia (due to lack of movement), delayed wound healing, and dislocation.
• Late Post-Operative: Loosening of components, wearing down of hardware, or periprosthetic fractures (fractures around the stem of the implant).
• Dislocation Risk Factors: Age $80+$, previous hip surgery, RA, posterior approach, and preoperative muscle weakness.

Questions & Discussion

• Question: Is that a muscle weakness or tightness? (Regarding the leg drop in side-lying test)
• Response: In the demonstration, the leg was dropping because the posterior fibers of the gluteus medius were weak, and the $TFL$ was taking over (dominance).
• Muscle Recruitment Test: A student volunteer (Mark) demonstrated a prone hip extension.
  • Observation: The hamstrings contracted before the glutes, which is considered a failure in proper movement patterns.
  • Correction: Fix by having the patient bend the knee to $90^{\circ}$ (shortening hamstrings into active insufficiency) and squeezing the glutes before lifting the leg. Practice leads to spontaneous correction of the movement pattern.
• Leg Length Discussion: True discrepancies are measured via weight-bearing X-rays; clinical tape measure is an approximation. A $1\,cm$ discrepancy is more significant on a smaller person ($1.5\,cm$ is often a threshold).
• Equipment Story: The instructor mentioned a clinic having a "half a car" inside to practice vehicle transfers with post-op patients.