Extensile proximal exposure of the stiff and ankylosed knee for revision TKA — trans-tendinous lengthening that spares the patellar tendon
- There is no internervous plane — the snip and V-Y are trans-tendinous extensions of the medial parapatellar arthrotomy through the femoral-nerve-supplied quadriceps tendon.
- The quadriceps snip is a single oblique cut at about 45 degrees from the arthrotomy apex; it has minimal effect on extensor power and needs no change to rehabilitation.
- The V-Y turndown gives greater exposure and lengthens the extensor mechanism, but risks extensor lag and patellar devascularisation.
- Both approaches exist to spare the patellar tendon from avulsion — never force eversion of a stiff patella.
- Escalate logically: lengthen arthrotomy and lateral release, then quadriceps snip, then V-Y turndown or tibial tubercle osteotomy.
When & Why
What it exposes. The quadriceps snip and the V-Y turndown are proximal, soft-tissue, extensile extensions of the standard medial parapatellar arthrotomy. They lengthen the extensor mechanism proximally so that the patella can be delivered and the joint exposed in the stiff or ankylosed knee — most often in revision total knee arthroplasty — without ever avulsing the patellar tendon from the tibial tubercle. Why these approaches are chosen. In the stiff knee the extensor mechanism is short, scarred and tethered. The defining danger of forcing exposure is avulsion of the patellar tendon from the tibial tubercle — a catastrophic, hard-to-repair complication that ruins the outcome. The snip and V-Y buy the translation needed to deliver the patella proximally, so its distal insertion is never placed under avulsing tension. They are proximal extensile (soft-tissue) manoeuvres; the alternative, a tibial tubercle osteotomy, achieves the same goal with a bony cut. Primary indications
- Revision total knee arthroplasty where exposure is difficult — stiffness, patella baja, multiple prior scars, or well-fixed components to be removed
- Primary TKA in the ankylosed or severely stiff knee where the patella cannot be safely everted or lateralised through a standard medial parapatellar arthrotomy
- Arthrofibrosis requiring open arthrolysis when the extensor mechanism will not deliver
- Complex distal femoral fractures (or non-unions) needing extensile anterior exposure
- Stiff septic knee requiring thorough washout and debridement
- Correction of patella infera (baja) where lengthening of the extensor mechanism is part of the plan Contraindications and relative cautions
- Active deep peri-articular infection at the intended incision (consider staged management)
- Severe compromise of the overlying soft-tissue envelope from multiple previous scars (plan skin bridges carefully)
- A grossly osteoporotic or severely comminuted patella increases the risk of further fragmentation with the V-Y turndown
- A patient unable to comply with the brace-protected rehabilitation required after a V-Y turndown Alternative and complementary approaches
- Standard medial parapatellar arthrotomy (von Langenbeck / Insall): the default; extended proximally as far as possible first
- Lateral retinacular release and patellofemoral ligament division: routinely added to allow lateral subluxation rather than full eversion
- Tibial tubercle osteotomy (Whiteside): the bony extensile option when soft-tissue lengthening is insufficient
- Subvastus / midvastus approaches: rarely adequate for the truly stiff revision knee but used in select primary cases The three proximal extensile options compared
| Option | What is cut | Exposure gained | Key trade-off |
|---|---|---|---|
| Quadriceps snip | Single oblique cut in quadriceps tendon | Moderate — delivers most stiff knees | Minimal; no rehab change |
| V-Y turndown | Full inverted-V quadriceps flap, turned down | Large, plus lengthening | Extensor lag; patellar devascularisation |
| Tibial tubercle osteotomy | Bone cut of the tubercle (Whiteside) | Very large proximal access | Nonunion; hardware prominence; fracture |
Position and landmarks. These are anterior exposures performed supine on a standard operating table, exactly as for a primary knee arthroplasty — no special table is required, but the ability to flex and extend the hip and knee freely is essential, because it is the repeated flexion that tests whether the extensor mechanism now delivers without undue tension. Use a bolster or leg holder so the knee holds 70 to 90 degrees of flexion without an assistant, a high-thigh tourniquet exsanguinated and inflated to the usual knee pressure, and have an image intensifier available for revision cases. Key landmarks - Patella and patellar tendon — the central reference; the tendon insertion onto the tibial tubercle is the structure you are protecting
- Tibial tubercle (tuberosity) — the distal anchor of the extensor mechanism; never avulse it by forceful eversion
- Quadriceps tendon — broad and palpable above the patella; this is where the snip and the V-Y limbs are placed
- Vastus medialis obliquus (VMO) — its distal edge meets the quadriceps tendon medially; the medial parapatellar arthrotomy runs along this junction
- Vastus lateralis — its distal fibres define the lateral extent of the quadriceps tendon for the snip and the V-Y lateral limb
- Gerdy's tubercle — anterolateral tibial insertion of the iliotibial band; relevant to the lateral limb of the V-Y The skin incision is a longitudinal anterior midline cut through the most suitable previous scar, extending a hand's breadth above the superior pole of the patella (so the snip or V-Y limbs sit in healthy tendon) and distally to just below the tibial tubercle.
When several longitudinal scars exist, use the most lateral usable scar as the skin incision. The blood supply to the anterior knee skin enters from the medial side (via branches of the saphenous and superficial femoral systems), so a lateral-based incision leaves the broad anterior skin flap with its medial blood supply intact and lowers the risk of wound edge necrosis.
The Exposure
The exposure is built around a single idea: lengthen the extensor mechanism proximally, through tendon, so the patella delivers without stressing its distal insertion. Work through the standard medial parapatellar arthrotomy first, test whether the patella delivers, and only then escalate — first to the quadriceps snip, and if that is insufficient, to the V-Y turndown.
Intra-operative photograph of an extensile anterior knee exposure showing the oblique quadriceps (rectus) snip at about 45 degrees from the apex of the medial parapatellar arthrotomy, directed proximolaterally across the quadriceps tendon, with the patella lateralised and the stiff knee joint exposed.
Context: A verified image is being sourced for this exposure.
Anatomy of the extensor mechanism. The quadriceps tendon is the confluence of four muscle bellies, all innervated by the femoral nerve, that inserts into the base (superior pole) of the patella and, via the patellar tendon, into the tibial tubercle.
| Component | Attachment / course | Functional note |
|---|---|---|
| Rectus femoris | Biarticular (anterior inferior iliac spine to quadriceps tendon); lies superficial and central | Only two-joint quadriceps head; its tendon is the superficial central band of the quadriceps tendon |
| Vastus medialis | Medial femur to quadriceps tendon and superomedial patella | Distal fibres (VMO) stabilise the patella against lateral subluxation |
| Vastus lateralis | Lateral femur to superolateral patella and tendon | Its distal edge defines the lateral border of the quadriceps tendon |
| Vastus intermedius | Anterior femoral shaft, deep to rectus | Deep layer; blends into the deep surface of the tendon |
| Vessel | Contribution | Relevance to these approaches |
|---|---|---|
| Superior lateral genicular artery | Principal supply to the proximal two-thirds of the patella | At risk with the lateral limb of a V-Y; its loss is the mechanism of patellar devascularisation |
| Superior and inferior medial genicular arteries | Medial third and distal pole | Compromised by the standard medial parapatellar arthrotomy itself |
| Inferior lateral genicular artery | Distal lateral patella and part of the tendon | At risk with extensive lateral release |
| Anterior tibial recurrent artery | Inferior pole via the fat pad | Contributes to the distal supply |
| Mid-patellar vessels (Scapinelli) | Enter directly through the middle of the anterior surface via the quadriceps insertion | Vulnerable when the quadriceps insertion is detached, as in a V-Y |
Exposure sequence
- A longitudinal anterior midline incision through the most suitable previous scar, extending a hand's breadth above the superior pole of the patella and distally to just below the tibial tubercle.
- Raise thin medial and lateral flaps in the subcutaneous plane to expose the extensor mechanism.
- Perform the standard medial parapatellar (Insall) arthrotomy: along the quadriceps tendon just medial to the midline, around the medial border of the patella, and along the medial border of the patellar tendon.
- Attempt to deliver the patella with the knee flexed; perform adhesiolysis, remove medial and lateral osteophytes, and add a lateral release dividing the lateral patellofemoral ligament.
- If the patella delivers and the joint is adequately exposed, proceed — no extensile step is needed.
- If the patellar tendon is under tension, or the patella will not evert or lateralise, escalate to the quadriceps snip. Never force a stiff patella.
- From the proximal apex of the medial parapatellar arthrotomy in the quadriceps tendon, make a single oblique incision at about 45 degrees, directed proximally and laterally across the full thickness of the quadriceps tendon, toward the interval between rectus femoris and vastus lateralis.
- The obliquity lengthens the tendon along a long, well-vascularised fibre line; the muscle bellies stay intact and innervated, so the deficit is small.
- Flex the knee and again attempt to deliver the patella. In most stiff knees the snip alone provides enough length for the patella to be everted or lateralised without tension on the tibial tubercle.
- If it does, proceed with the procedure — the snip will be closed side-to-side at the end. The snip is intentionally conservative and should be used readily whenever exposure is borderline.
- When the snip is insufficient, convert it into an inverted-V (Coonse-Adams). From the same apex, extend the superolateral limb further across the quadriceps tendon toward vastus lateralis, and add a superomedial limb directed proximally and medially.
- This completes an inverted V with its apex pointing distally, creating a distally-based quadriceps flap still attached to the patella.
- Reflect the quadriceps flap distally with the patella, exposing the anterior distal femur and the joint widely. Stay on bone and capsule; protect the underlying structures.
- Perform the intended procedure — component extraction, arthrolysis, or fixation. Add only the length needed to relieve tension on the tibial tubercle: every millimetre of length added is a millimetre of potential extensor lag.
- Snip: close the oblique cut side-to-side with strong non-absorbable interrupted sutures (a number 2 or 5 braided polyester), tested through a range of motion. No brace; standard rehabilitation unchanged.
- V-Y: close the apex of the V first (reconstituting the central vertical limb), then close each oblique limb, converting the V into a Y and setting the lengthening. Brace in extension for about six weeks with protected, gradually increasing flexion; avoid active resisted extension against gravity.
- Confirm the repair holds through a functional arc and the patella tracks without undue tension before final skin closure.
The quadriceps snip is essentially a single superolateral oblique limb; the V-Y turndown adds a superomedial limb to make a full inverted-V flap that is turned down and then closed as a Y to lengthen the tendon. The snip trades almost nothing; the V-Y trades exposure and length for extensor lag and patellar devascularisation risk.
Dangers & Extensions
Structures at risk, by layer
| Layer | Structure | Risk and protection |
|---|---|---|
| Skin / subcutaneous | Anterior skin flap vascularity (medially based) | Use the most lateral usable scar; avoid raising broad superficial flaps |
| Superficial | Infrapatellar branch of saphenous nerve (medial skin) | Numbness expected medially; minimise distal medial dissection; counsel pre-operatively |
| Extensor mechanism | Quadriceps tendon (the intended cut) | Repair meticulously — this is the intended structure, not a complication |
| Extensor mechanism | Patellar tendon | Never avulse — the whole point of the approach; if under tension, escalate exposure |
| Patella | Peripatellar vascular ring (superior lateral genicular and mid-patellar vessels) | Avoid combining full medial, lateral and proximal stripping (V-Y); prefer the snip |
| Deep posterior | Popliteal vessels and nerve (posterior to capsule, in flexion) | Stay on bone and capsule; careful posterior releases; beware the fixed flexed knee |
The structure the whole approach exists to protect. Forcing eversion of a stiff patella can avulse the tendon from the tibial tubercle — a catastrophic, difficult-to-repair injury. If the tendon is ever under tension during exposure, stop and escalate up the ladder.
The patella depends on a peripatellar ring (superior lateral genicular, superior and inferior medial genicular, mid-patellar vessels). Combining a medial arthrotomy, an extensive lateral release and a V-Y that detaches the quadriceps insertion can devascularise the patella, risking osteonecrosis. Prefer the snip and minimise lateral release when a V-Y is used.
A sensory nerve crossing the medial knee superficially. Numbness over the medial proximal tibia is common and expected after any medial arthrotomy. It is not a motor deficit; counsel patients pre-operatively.
Lies posterior to the capsule and is at risk during posterior capsular release and component extraction in flexion. Stay on bone and capsule, use careful posterior dissection, and beware the fixed flexed knee where the bundle sits closer to the posterior capsule.
Extensile options. Both the snip and the V-Y lie in the quadriceps tendon, which can be extended further proximally along the femur if more proximal exposure is required (a distal femoral fracture, a long-stem revision) — the oblique limbs simply continue superiorly, though the further proximally one goes, the more the superior lateral genicular supply to the patella is placed at risk. Distally the standard arthrotomy continues along the medial border of the patellar tendon to the tibial tubercle; when the soft-tissue options are exhausted, a tibial tubercle osteotomy is the distal bony extensile step. A snip can be converted intra-operatively into a V-Y by adding the superomedial limb, and a V-Y that is still insufficient can be supplemented by a TTO — escalation is always in one direction, from least to most morbid. Complications
| Complication | Prevention | Management |
|---|---|---|
| Patellar tendon avulsion | Escalate exposure before tension builds; use snip / V-Y / TTO | Primary repair with suture anchors or tension band; protect in extension; poor prognosis |
| Patellar devascularisation | Prefer the snip; limit lateral release with V-Y | Avoid further patellar surgery; monitor for osteonecrosis |
| Skin flap necrosis | Use the most lateral usable scar; raise flaps carefully | Wound care, plastic surgery input if full-thickness |
| Inadequate exposure | Escalate the ladder rather than force exposure | Convert snip to V-Y, or add a TTO |
| Complication | Risk factor | Prevention / note |
|---|---|---|
| Extensor lag | Lengthening, especially with V-Y | Add only necessary length; brace and rehabilitate; often improves with therapy |
| Quadriceps weakness | Greater with V-Y than snip | Progressive strengthening; the snip preserves most power |
| Stiffness / arthrofibrosis | Prolonged immobilisation | Early motion where the repair allows (snip: immediate; V-Y: protected) |
| Patellar osteonecrosis | Combined vascular insult | Minimise combined releases; observe |
| Infection | Large exposure, long case | Routine prophylaxis; meticulous soft-tissue handling |
Rehabilitation. After an isolated quadriceps snip there is no brace and no change to the standard knee arthroplasty protocol — weight bearing and range of motion proceed as for the underlying procedure, which is the principal advantage of the snip. After a V-Y turndown the knee is braced in full extension for about six weeks with gradual protected flexion, and active resisted extension against gravity is avoided during the protected period. For comparison, after a tibial tubercle osteotomy a cylinder cast or brace in extension is used for about six weeks with no active extension for six weeks to protect the osteotomy. DVT prophylaxis, wound monitoring, and documenting any extensor lag apply throughout. Outcomes. The snip is consistently reported to have minimal effect on extensor mechanism function — quadriceps strength and active extension are largely preserved, range of motion is not compromised relative to the underlying procedure, and no special rehabilitation is required, which underpins its place as the default first extensile step. The V-Y reliably delivers the exposure and lengthening for which it is designed, but at the cost of a measurable extensor lag and reduced quadriceps strength proportional to the length added; functional outcomes are acceptable when lengthening is modest and rehabilitation disciplined, but the lag may persist. Patellar devascularisation is recognised but less common.
For the quadriceps snip: essentially no functional trade-off — minimal effect on extensor power and no change to rehabilitation. For the V-Y turndown: the trade-off is extensor lag and patellar devascularisation risk, balanced against greater exposure and the ability to lengthen a contracted extensor mechanism. State both trade-offs explicitly when discussing the approach.
Procedures Through This Approach
- Revision total knee arthroplasty, including extraction of well-fixed components and re-implantation
- Primary TKA in the ankylosed or arthrodesed-in-extension knee
- Open arthrolysis for marked arthrofibrosis
- Extensile anterior fixation of complex distal femoral fractures and non-unions
- Debridement and washout of the stiff septic knee
- Lengthening of a contracted extensor mechanism for patella baja
Viva & Exam Focus
QUAD SNIPQUAD SNIP — the steps
ESCALATEESCALATE — the exposure ladder for the stiff knee
VY TURNDOWNV-Y TURNDOWN — dangers and principles
Q: How is the quadriceps snip performed? From the proximal apex of the medial parapatellar arthrotomy, a single oblique incision is made at about 45 degrees, directed proximally and laterally across the full thickness of the quadriceps tendon toward the interval between rectus femoris and vastus lateralis.
Q: What is the internervous plane of the quadriceps snip and V-Y turndown? There is no internervous plane. Both are trans-tendinous extensions of the medial parapatellar arthrotomy through femoral-nerve territory; the cut is safe because it divides tendon while the muscle bellies remain innervated on either side.
Q: What is the effect of the quadriceps snip on extensor power and rehabilitation? The snip has a minimal effect on extensor power and requires no change to the standard rehabilitation protocol. This contrasts with the V-Y turndown, which lengthens the tendon and risks an extensor lag requiring brace-protected rehabilitation.
Q: What are the principal disadvantages of the V-Y quadricepsplasty? An extensor lag (because the tendon is deliberately lengthened) and the risk of patellar devascularisation (by compromising the superior lateral genicular and mid-patellar vessels), which may lead to patellar osteonecrosis.
Q: How does the quadriceps snip / V-Y differ from a tibial tubercle osteotomy? The snip and V-Y are soft-tissue extensile options (trans-tendinous), whereas a tibial tubercle osteotomy is a bony option (an osteotomy of the tubercle, re-fixed with screws). The TTO carries risks of nonunion, hardware prominence and tibial fracture that the soft-tissue options do not.
Q: Why are these proximal extensile steps performed at all? To gain exposure and translation of the extensor mechanism in the stiff knee without avulsing the patellar tendon from the tibial tubercle — a catastrophic, hard-to-repair injury. Lengthening proximally relieves tension on the tendon distally.
The snip and V-Y have no internervous plane. Both are trans-tendinous extensions of the medial parapatellar arthrotomy through the quadriceps tendon, all supplied by the femoral nerve. The cut is safe because it divides tendon while the muscle bellies remain innervated either side.
A single oblique cut at about 45 degrees from the arthrotomy apex, directed proximolaterally. Minimal effect on extensor power and no change to rehabilitation — no brace, standard protocol. This is why it is the default first extensile step.
The V-Y lengthens the extensor mechanism, giving greater exposure, but produces an extensor lag proportional to the length added. It needs brace-protected rehabilitation for about six weeks. Add only the length needed to relieve tension on the tibial tubercle.
The patella depends on a peripatellar ring — principally the superior lateral genicular artery and the mid-patellar vessels entering via the quadriceps insertion. A V-Y that detaches the quadriceps insertion, combined with medial and lateral releases, risks patellar osteonecrosis. Prefer the snip; limit combined releases.
These approaches exist to spare the patellar tendon from avulsion. Never force eversion of a stiff patella. If the tendon comes under tension during exposure, stop and escalate up the ladder.
The snip and V-Y are soft-tissue extensile options; a tibial tubercle osteotomy is a bony option. Choose the TTO when extensive proximal access to well-fixed components or stems is needed. State the rationale explicitly: lengthening favours V-Y, proximal bony access favours TTO.
Exam viva scenarios
Practise clinical reasoning and management decisions out loud
“You are revising a total knee replacement. Through a standard medial parapatellar arthrotomy with a lateral release, the patella will not deliver and the patellar tendon is visibly under tension. How do you proceed?”
“Compare and contrast the quadriceps snip, the V-Y turndown and the tibial tubercle osteotomy as extensile exposures for the knee. How do you choose between them?”
“Describe the relevant anatomy of the extensor mechanism for these approaches, and explain why a trans-tendinous cut is safe.”
Purpose
- Proximal, soft-tissue, extensile exposure of the stiff and ankylosed knee
- Lengthen the extensor mechanism proximally to spare the patellar tendon
- Most often used in revision TKA and TKA in the ankylosed knee
- Performed after standard arthrotomy plus lateral release is insufficient
The quadriceps snip
- Single oblique cut at about 45 degrees from the arthrotomy apex
- Directed proximally and laterally across the quadriceps tendon
- Trans-tendinous — no internervous plane (femoral nerve territory)
- Minimal effect on extensor power; no brace; no change to rehab
- Repaired side-to-side with strong non-absorbable sutures
The V-Y turndown (Coonse-Adams)
- Inverted-V: superolateral limb plus added superomedial limb, apex distal
- Distally-based quadriceps flap turned down for wide exposure
- Closed as a Y to lengthen the extensor mechanism
- Trade-off: extensor lag (proportional to length added)
- Trade-off: patellar devascularisation risk; brace in extension about 6 weeks
No internervous plane
- Both snip and V-Y are trans-tendinous extensions of the medial parapatellar arthrotomy
- All quadriceps heads supplied by the femoral nerve
- Cut is safe because muscle bellies remain innervated either side
- The parent medial parapatellar arthrotomy likewise has no true internervous plane
Escalation ladder
- Extended medial parapatellar arthrotomy, adhesiolysis, osteophyte removal
- Lateral release / patellofemoral ligament division; lateral subluxation not eversion
- Quadriceps snip — the default first extensile step
- V-Y turndown or tibial tubercle osteotomy for the most ankylosed knees
- V-Y when lengthening is wanted; TTO when proximal bony access is needed
Structures at risk
- Patellar tendon — the structure the approach exists to protect from avulsion
- Patellar blood supply — superior lateral genicular and mid-patellar vessels (V-Y)
- Infrapatellar branch of saphenous nerve — medial numbness, expected
- Popliteal neurovascular bundle — in flexion during posterior work, stay on bone
- Anterior skin flap vascularity — use most lateral usable scar
Contrast with TTO
- Snip and V-Y are soft-tissue options; TTO is a bony option
- TTO: osteotomy of the tubercle, re-fixed with screws
- TTO gives powerful proximal access to well-fixed components or stems
- TTO risks: nonunion, hardware prominence, tibial fracture
- Lengthening favours V-Y; proximal bony access favours TTO
References
Guidelines, registries and global practice. Exposure of the difficult knee in revision arthroplasty is managed by convergent principles across examination systems. The graduated strategy — adequate standard exposure and lateral release, then a quadriceps snip, then a V-Y turndown or tibial tubercle osteotomy — is taught universally and reflects the landmark descriptions below.
| Body | Position on extensile exposure of the difficult knee |
|---|---|
| AAOS (US) | Patellar tendon avulsion is a catastrophic complication; lengthen the extensor mechanism proximally; use the graduated exposure ladder |
| BOA / NICE (UK) | Meticulous soft-tissue handling; plan skin incisions around previous scars; consent for possible extensile steps and brace-protected rehabilitation |
| AO Foundation | Extensile anterior exposure for complex distal femoral fractures follows the same trans-tendinous lengthening principles |
For the operative surgery and oral examination, describe the quadriceps snip and V-Y turndown systematically: the trans-tendinous (no-internervous-plane) anatomy, the 45-degree proximal-lateral snip, the inverted-V to Y-lengthening of the turndown, the structures at risk (patellar tendon, patellar blood supply, popliteal bundle), and the graduated ladder ending in a tibial tubercle osteotomy. State the trade-offs of each step explicitly.
A New Operative Approach to the Knee Joint
- The original description of the inverted-V (V-Y) quadricepsplasty for extensile exposure of the knee
- A distally-based quadriceps tendon flap is created and turned down to expose the joint without detaching the tibial tubercle
- Established the principle of proximally lengthening the extensor mechanism to gain safe exposure
- The foundation on which later modifications (snip, Scott modification) were built
The Use of a Modified V-Y Quadricepsplasty During Total Knee Replacement to Gain Exposure and Improve Postoperative Flexion
- Described a modified V-Y quadricepsplasty used during total knee replacement for the stiff knee
- Used both to gain intra-operative exposure and to improve postoperative flexion by lengthening the extensor mechanism
- Defined the practical technique and the place of the V-Y within the exposure strategy
- Reported the trade-off of extensor mechanism lengthening against postoperative lag
Exposure in Difficult Total Knee Arthroplasty Using Tibial Tubercle Osteotomy
- Described tibial tubercle osteotomy with a distal cortical hinge for extensile exposure in difficult total knee arthroplasty
- The bony osteotomy allows proximal translation of the entire extensor mechanism for wide exposure
- Re-fixation is achieved with screws, with protection of the osteotomy during healing
- Defined the bony alternative to the soft-tissue quadriceps snip and V-Y for the most difficult exposures
Surgical Exposures in Revision Total Knee Arthroplasty
- Systematic review of exposure options in revision total knee arthroplasty
- Advocates a graduated strategy from the standard medial parapatellar arthrotomy through the quadriceps snip to the V-Y and tibial tubercle osteotomy
- The quadriceps snip is highlighted as the preferred first extensile step because of its minimal morbidity
- Defines the decision framework between the soft-tissue and bony extensile options
Blood Supply of the Human Patella: Its Relevance to Pathology and Surgery
- Detailed the peripatellar anastomotic vascular ring supplying the patella
- The mid-patellar vessels enter the anterior surface through the quadriceps tendon insertion and supply the proximal two-thirds
- The principal named contributor is the superior lateral genicular artery
- Explained why detachment of the quadriceps insertion risks devascularisation and osteonecrosis of the patella